Hi Don,
I bought a 70's SVT head here in Lima Perú, it's a 220 head, and needs work, but the price was right, $300.00. I went to technical school about twenty years ago, so I'm not a complete novice and have done some work on SVT's before.
My two main problems are: someone put 6L6's in it instead of 6550's, was that an extensive mod including wiring changes at the tube sockets and voltage changes, or a simple swap with bias adjustment? And if it was extensive would you have an idea how it was done, and how it could be reversed? (my schematic is at home in an unknown place) How much do you think the output wattage was reduced in the process? Everything looks original in it except for the power tube change. The owner told me it was changed over about two years ago, and still knows the tech who did it.
Also it is going to need new electrolytic caps, with new ones is it a must to bring up the voltage slowly with a variac? If so, would running it at 110 VAC for a few seconds help as I do not have a variac at my disposal.
For some reason, the back lower plate is identical to a 110 volt head, since it is running at 220 volts should I put a 5 amp fuse in it instead of a 10 amp fuse? (it still says 10 amp fuse)
Do you know of a good place to get the cans for this amp online? How much should I expect to pay for these? BTW it sounds great the way it is except that it has some original Magnavox 12DW7's in it that are unbelievably microphonic and distorted.
Help! I have many SVT questions.
Moderator: jingle_jangle
Bob, Angela Instruments is a good place to get caps for guitar amps: www.angela.com or 301-725-0451.
An amp that old could use signal cap upgrades as well. Check out the Angela Tin Caps. Semi-noble metal foils might really make a difference. Any ceramic disc caps need to come out. I wouldn't go for less than Sprague Orange Drop caps: Polyesters = warmer tone, Polypropylene = neutral tone. Sprague caps should be available anywhere. I have polyester film caps in my old Heathkit amps, and they work well in the old vintage gear that isn't high end by modern standards.
Don would have to advise on any wiring changes, as second guessing another tech's work sight unseen is not for me. Angela's prices are about as good as anywhere you'll find for premium caps and Hammond transformers. Sprague caps are very good value for the money.
Check out Parts Express for caps if you want the lowest prices and the least advice. I'm just letting you know where to order some caps so you can get started; I wouldn't hazard a guess on the 6L6 vs. 6550 issue. Steve Melkithesian at Angela Instruments can also probably advise you on the tube conversion issues if you're in a hurry and can't wait for Don's answer here. I'd have that amp opened up if I called Steve, because he'll shoot you some questions right back. Check out Steve's NOS tubes if you're in the website. I got some NOS RCA 6C4 tubes used in the new C-J PV-14L and some old Ampeg amps for only $9 each. I bought a quad just to add to my stash of NOS M8080 Mullards. The M8080/CV4058 Mullard is the best 6C4 type tube there ever was, so get some, Bob, if your Ampegs use them. C-J put them in my PV-14L (and that's a $2K preamp), and they claim it's the best 6C4 they ever heard, and Watford Valves says the same. About $12 each from Watford before "carriage", and they are "mil spec" surplus.
An amp that old could use signal cap upgrades as well. Check out the Angela Tin Caps. Semi-noble metal foils might really make a difference. Any ceramic disc caps need to come out. I wouldn't go for less than Sprague Orange Drop caps: Polyesters = warmer tone, Polypropylene = neutral tone. Sprague caps should be available anywhere. I have polyester film caps in my old Heathkit amps, and they work well in the old vintage gear that isn't high end by modern standards.
Don would have to advise on any wiring changes, as second guessing another tech's work sight unseen is not for me. Angela's prices are about as good as anywhere you'll find for premium caps and Hammond transformers. Sprague caps are very good value for the money.
Check out Parts Express for caps if you want the lowest prices and the least advice. I'm just letting you know where to order some caps so you can get started; I wouldn't hazard a guess on the 6L6 vs. 6550 issue. Steve Melkithesian at Angela Instruments can also probably advise you on the tube conversion issues if you're in a hurry and can't wait for Don's answer here. I'd have that amp opened up if I called Steve, because he'll shoot you some questions right back. Check out Steve's NOS tubes if you're in the website. I got some NOS RCA 6C4 tubes used in the new C-J PV-14L and some old Ampeg amps for only $9 each. I bought a quad just to add to my stash of NOS M8080 Mullards. The M8080/CV4058 Mullard is the best 6C4 type tube there ever was, so get some, Bob, if your Ampegs use them. C-J put them in my PV-14L (and that's a $2K preamp), and they claim it's the best 6C4 they ever heard, and Watford Valves says the same. About $12 each from Watford before "carriage", and they are "mil spec" surplus.
Thanks Phil,
yes it does use one 6C4, I think I will try those, and thanks for the website. what I really need are (4) 12DW7's which are kind of expensive, and two 12BH7 driver tubes. Supposedly there is a tech here who has them for about 6 to 9 dollars which is very cheap, there are a lot of used tubes here so that may be the case. BTW there were three original Magnavox pre amp tubes in it! no wonder they were microphonic, and actually that does not describe the howl I got from them, oscillation is a better term.
I have not been able to find any information on the web concerning the tube conversion which I'm sure was done because someone had some old 6L6's hanging around that got pulled from old Fender amps, I can even see marks on the bases of two of them from the clamps with teeth that Fender used in the old upside down chassis's. The guy I bought it from still knows where the tech is that did it, so if worst comes to worst I'll contact him and see what he did.
I always thought RCA tubes were the best, I used to buy them for my SVT's, they always lasted for years and sounded good.
Ever here of Teisco amps? I'm using a 100 watt head for practise with a double 15 cab, it sounds great, the owner said it was German, it has 4 6L6's for output. It even has a watt meter on it, is is a funky looking old head. It has volume and tone, haha! and a knob that says expander on it, what it does is thin out the sound. the setup has a great fat tone, talk about a great low E sound, it's ported and the frequency has to be lower than an E because the lower you go the thicker it gets. It also has good mid response.
yes it does use one 6C4, I think I will try those, and thanks for the website. what I really need are (4) 12DW7's which are kind of expensive, and two 12BH7 driver tubes. Supposedly there is a tech here who has them for about 6 to 9 dollars which is very cheap, there are a lot of used tubes here so that may be the case. BTW there were three original Magnavox pre amp tubes in it! no wonder they were microphonic, and actually that does not describe the howl I got from them, oscillation is a better term.
I have not been able to find any information on the web concerning the tube conversion which I'm sure was done because someone had some old 6L6's hanging around that got pulled from old Fender amps, I can even see marks on the bases of two of them from the clamps with teeth that Fender used in the old upside down chassis's. The guy I bought it from still knows where the tech is that did it, so if worst comes to worst I'll contact him and see what he did.
I always thought RCA tubes were the best, I used to buy them for my SVT's, they always lasted for years and sounded good.
Ever here of Teisco amps? I'm using a 100 watt head for practise with a double 15 cab, it sounds great, the owner said it was German, it has 4 6L6's for output. It even has a watt meter on it, is is a funky looking old head. It has volume and tone, haha! and a knob that says expander on it, what it does is thin out the sound. the setup has a great fat tone, talk about a great low E sound, it's ported and the frequency has to be lower than an E because the lower you go the thicker it gets. It also has good mid response.
Bob, I never heard of Teisco amps. They probably went the way of Viking snowmobiles in the 70's. Mullards are killer tubes. My M8080's even came with little plastic pin caps that protect the pins from bending. I also got a pair of Mullard GZ37/CV378 rectifiers for $66. Talk about gorgeous tubes!
If you can find a wiring schematic on the internet that shows how the original 6550's were wired in the SVT, you can just follow that to set it straight.
12DW7 tubes are being manufactured again in eastern Europe. Ampeg owners can rejoice. ALSO, the 6C4 is basically half of a 12AU7 medium mu twin triode. You can replace two 6C4's with a single 12AU7, or wire a 12AU7 in parallel for double the current drive and less output impedance. My homebrew preamp uses 12AU7 tubes in the linestage section, and my Heathkit power amps use a 12AU7 for the input gain stage and driver, and another for the phase splitter. The 12AU7 was largely overlooked in guitar amps. The 12AU7 can achieve wider bandwidth because of the lower gain and much lower output impedance over a 12AX7. The M8080/CV4058 was actually the transmitter output power tube in British army portable radios and can dissipate something like 5 watts. Doing preamp duty is child's play to it. It had a 10,000 hour rated lifespan in portable transmitter power output duty, so no telling how long it can last in your SVT as a preamp tube. I SERIOUSLY doubt that the Russians will ever make anything equal to it, so grab some Mullards while you can. Thankfully, the demand is low or the supply would have been exhausted and the prices sky high.
12BH7 tubes should be no problem to get. And yes, the RCA 6C4 tubes look good, but the Mullards look better.
If you can find a wiring schematic on the internet that shows how the original 6550's were wired in the SVT, you can just follow that to set it straight.
12DW7 tubes are being manufactured again in eastern Europe. Ampeg owners can rejoice. ALSO, the 6C4 is basically half of a 12AU7 medium mu twin triode. You can replace two 6C4's with a single 12AU7, or wire a 12AU7 in parallel for double the current drive and less output impedance. My homebrew preamp uses 12AU7 tubes in the linestage section, and my Heathkit power amps use a 12AU7 for the input gain stage and driver, and another for the phase splitter. The 12AU7 was largely overlooked in guitar amps. The 12AU7 can achieve wider bandwidth because of the lower gain and much lower output impedance over a 12AX7. The M8080/CV4058 was actually the transmitter output power tube in British army portable radios and can dissipate something like 5 watts. Doing preamp duty is child's play to it. It had a 10,000 hour rated lifespan in portable transmitter power output duty, so no telling how long it can last in your SVT as a preamp tube. I SERIOUSLY doubt that the Russians will ever make anything equal to it, so grab some Mullards while you can. Thankfully, the demand is low or the supply would have been exhausted and the prices sky high.
12BH7 tubes should be no problem to get. And yes, the RCA 6C4 tubes look good, but the Mullards look better.
Hi Phil,
I checked ou that site you gave me and it looks good, what do you think of the NOS tubes? they had both 12DW7's and 12BH7's, both were close to $20.00 though.
Oh that Teisco is Japanese and was made around 1967, it is a great head if you like dirty sound like I do. The expander control is I think two pots in one, the bass goes up while the treble goes down and vice versa, I like it, it is a real simple way of getting the sound you want quickly. I get a great Jack Bruce sound without a fuzzbox with it loud. The cab I'm using is also circa 1967, it's very tubby sounding but is great for classic rock, and the frequency response is very smooth. I can't wait to get the Ampeg up and running though.
I had a harrowing experience this morning, I fixed one of my little Ampegs the other day and never checked it out. This morning I was half asleep and plugged it into the 220 wall outlet to check it out, and of course bzzzt!, and I had to leave right away so all day I didn't know if I just blew the fuse (it's internal) or the transformer, luckily it was just the fuse, Ampegs are great amps, you can double the voltage and they keep right on playing, haha. Doing that has been one of my nightmares, because who in the states has to remember to plug their amp into a stepdown transformer before they turn it on? They are everywhere here, half of the appliances are from Japan or the USA. I hope that will jog my memory from now on when I plug my amps in, luckily the SVT is 220.
I checked ou that site you gave me and it looks good, what do you think of the NOS tubes? they had both 12DW7's and 12BH7's, both were close to $20.00 though.
Oh that Teisco is Japanese and was made around 1967, it is a great head if you like dirty sound like I do. The expander control is I think two pots in one, the bass goes up while the treble goes down and vice versa, I like it, it is a real simple way of getting the sound you want quickly. I get a great Jack Bruce sound without a fuzzbox with it loud. The cab I'm using is also circa 1967, it's very tubby sounding but is great for classic rock, and the frequency response is very smooth. I can't wait to get the Ampeg up and running though.
I had a harrowing experience this morning, I fixed one of my little Ampegs the other day and never checked it out. This morning I was half asleep and plugged it into the 220 wall outlet to check it out, and of course bzzzt!, and I had to leave right away so all day I didn't know if I just blew the fuse (it's internal) or the transformer, luckily it was just the fuse, Ampegs are great amps, you can double the voltage and they keep right on playing, haha. Doing that has been one of my nightmares, because who in the states has to remember to plug their amp into a stepdown transformer before they turn it on? They are everywhere here, half of the appliances are from Japan or the USA. I hope that will jog my memory from now on when I plug my amps in, luckily the SVT is 220.
Bob, you can check out my conversion of a Marshall AVT20 to an "all purpose" guitar amp in this forum. It does the dirty bass amp and dirty guitar amp thing really well, but since it has a 10" Eminence B102 extended range bass guitar speaker in it, you can also clean it up really well. It's just a practice amp at only 20 watts, unless you use the DI out feature and run through the mixing board and PA system. It does make the furniture rattle in a small room, however. If I had my "AVT20B" back in 76 instead of that Peavey 1x18 folded horn monster, it would have made practice a lot more fun. My brother seems to have taken a liking to the OLP MM2 and Marshall AVT20B setup. He likes the dirty bass tones also, and they do remind me of Jack Bruce bass tone on old Cream recordings.
Something you need to remember: if tubes were still being made in the USA today, you would have to pay $20 for good twin triode preamp tubes and $30 for good power tubes. When you find them for those prices, you aren't being ripped off. Angela has Philips 5881 tubes listed for $15 each at sale price, $18 regular price, last time I looked. I bought a quad just to add to my Tung-Sol 5881 stash in case I ever run out. I will probably just switch over to JJ 6L6GC tubes at $30/pair since they are claimed to be equal to NOS tubes.
I would stick with NOS 12DW7 tubes until I heard what the new production was like. $20 sounds like a good price to me. Angela has new Hammond transformers if you blow your Ampeg transformer. Their minimum shipping is $10 on anything, but they pack better than anybody else I have ever bought tubes from, except Conrad-Johnson which uses custom boxes with individual cutouts in a foam block for each tube in their complete matched sets. C-J is sitting on a mountain of tubes. Their design/business philosophy seems to be to buy up large bulk stashes of surplus preamp tubes suitable for audio amps at a cheap price when they become available and then design their new amps around those tubes. That's why their tube numbers can seem a bit strange compared to everybody else (quick, tell me what a 5965 or 6FQ7 tube is comparable to), but their amps sound fabulous because they have the hot tubes. They cherry pick the best, sell the rest to the next tier of resellers (another source of profits), and get a hefty markup on their matched sets. You would have thought some guitar amp manufacturers would have copped their design/sales strategy, but maybe guitarists are afraid of anything but a 12AX7/6L6 or EL34 combo. Old Ampegs seem to be an exception, so at least they ONCE had a designer that was on the ball. The 6550 (or KT88) was what you wanted for bass amps, and one of very few tubes ever specifically designed for high fidelity audio amp duties (two others were the 300B and KT66, which are still rare in guitar amps). Bill Conrad and Lew Johnson are ECONOMISTS by training and original profession, not electrical/acoustical engineers as they just hire out that part of the business. In effect, their amps were designed to use some of the best preamp tubes ever (that were overlooked during the hollowstate heyday as most manufacturers used the cheapest tubes available) that you will likely find only from them in matched sets in the future. You have to buy up huge stashes at dirt cheap prices and sell to fanatics at much higher prices in the future, but it's made for some great amps using tubes that were largely overlooked. Ampeg could have stashed away tons of 6C4 and 12DW7 tubes as well, but they are too much of a mass marketer for C-J's plan to work for them, and the tubes were not cheap surplus items when the amps were designed. If you like old Ampegs, I would build up a stash of tubes like the 6C4 while you can. The 6C4 is not a common audio tube, and it will not be brought back into production as the 12AU7 does the same thing, twice in the same package, but at 12 volts of filament power instead of 6 volts. A 6AU7 is also available from surplus dealers that might take the place of the 6C4 in a circuit with a socket changeout.
Something you need to remember: if tubes were still being made in the USA today, you would have to pay $20 for good twin triode preamp tubes and $30 for good power tubes. When you find them for those prices, you aren't being ripped off. Angela has Philips 5881 tubes listed for $15 each at sale price, $18 regular price, last time I looked. I bought a quad just to add to my Tung-Sol 5881 stash in case I ever run out. I will probably just switch over to JJ 6L6GC tubes at $30/pair since they are claimed to be equal to NOS tubes.
I would stick with NOS 12DW7 tubes until I heard what the new production was like. $20 sounds like a good price to me. Angela has new Hammond transformers if you blow your Ampeg transformer. Their minimum shipping is $10 on anything, but they pack better than anybody else I have ever bought tubes from, except Conrad-Johnson which uses custom boxes with individual cutouts in a foam block for each tube in their complete matched sets. C-J is sitting on a mountain of tubes. Their design/business philosophy seems to be to buy up large bulk stashes of surplus preamp tubes suitable for audio amps at a cheap price when they become available and then design their new amps around those tubes. That's why their tube numbers can seem a bit strange compared to everybody else (quick, tell me what a 5965 or 6FQ7 tube is comparable to), but their amps sound fabulous because they have the hot tubes. They cherry pick the best, sell the rest to the next tier of resellers (another source of profits), and get a hefty markup on their matched sets. You would have thought some guitar amp manufacturers would have copped their design/sales strategy, but maybe guitarists are afraid of anything but a 12AX7/6L6 or EL34 combo. Old Ampegs seem to be an exception, so at least they ONCE had a designer that was on the ball. The 6550 (or KT88) was what you wanted for bass amps, and one of very few tubes ever specifically designed for high fidelity audio amp duties (two others were the 300B and KT66, which are still rare in guitar amps). Bill Conrad and Lew Johnson are ECONOMISTS by training and original profession, not electrical/acoustical engineers as they just hire out that part of the business. In effect, their amps were designed to use some of the best preamp tubes ever (that were overlooked during the hollowstate heyday as most manufacturers used the cheapest tubes available) that you will likely find only from them in matched sets in the future. You have to buy up huge stashes at dirt cheap prices and sell to fanatics at much higher prices in the future, but it's made for some great amps using tubes that were largely overlooked. Ampeg could have stashed away tons of 6C4 and 12DW7 tubes as well, but they are too much of a mass marketer for C-J's plan to work for them, and the tubes were not cheap surplus items when the amps were designed. If you like old Ampegs, I would build up a stash of tubes like the 6C4 while you can. The 6C4 is not a common audio tube, and it will not be brought back into production as the 12AU7 does the same thing, twice in the same package, but at 12 volts of filament power instead of 6 volts. A 6AU7 is also available from surplus dealers that might take the place of the 6C4 in a circuit with a socket changeout.
Phil, 12DW7's were rare and expensive 25 years ago, as were 7027A's which they used in a lot of their amps. The original SVT power tube was an X-ray tube, I forget the number (7941?) it had the cathode on top of the tube like an old radio, they changed very quickly to 6550's. So Ampeg has never used the most common tubes either. the old SVT's can be converted very easily to 12AX7's instead of 12DW7's but I like the sound of the latter better and they have more gain too.
I used to use old Dynaco stereo 70's, did you ever own any of those? They have a nice sound but do not in any way even compare with the old tube Mac's. I had one MC-30 with a matching preamp. It was the best sounding audio amp I've ever heard, it had a silky sound to it, the likes of which I have never experienced since. It is very obvious why old Macintosh tube amps have skyrocketed in price, to me they are worth every penny, and I will buy an MC-275 as soon as I have 2 or 3 extra grand to blow on a power amp.
I used to use old Dynaco stereo 70's, did you ever own any of those? They have a nice sound but do not in any way even compare with the old tube Mac's. I had one MC-30 with a matching preamp. It was the best sounding audio amp I've ever heard, it had a silky sound to it, the likes of which I have never experienced since. It is very obvious why old Macintosh tube amps have skyrocketed in price, to me they are worth every penny, and I will buy an MC-275 as soon as I have 2 or 3 extra grand to blow on a power amp.
Bob, while some of those old power amps like McIntosh, Fisher, and EICO where fabulous for their days (and Marantz was better than any of them), they have been thoroughly eclipsed by more modern designs that use better components. C-J uses custom designed transformers now (transpectral) that are patented and of a wider bandwidth than those available in the past. The Dynaco amps were noted for having good output transformers, and there are lots of mods to upgrade the rest of the circuitry. C-J's solid state amps, like my MF-2250, will trounce the vast majority of modern tube amps even. My old Heathkits sound OK, but they are no match for modern amps, and they were notorious for blowing output transformers. A pair of Hammond trannies set me back $150 when they blew. It costs $100 just to retube the outputs with Russian KT66 tubes. Plus I have them down now awaiting new capacitors and resistors as well. My verdict is they are not worth it except as a collector's item. I would take a nice modern C-J Premier 11, MV-55, or MV-60 any day over one of those old vintage tube amps. I never knew solid state could sound so nice until I put the MF-2250 in my system. It uses FET's in the gain and driver stages, which are very similar to tubes. I got one in mint condition for $900 on eBay from an authorized dealer (retail $2300) and the sound blew me away.
I can get a new or like new MV-60 for a little over $2K if I shop around, or $2795 full retail. However, for bass freaks I believe the solid state MF-2250 or MF-2300 would surpass. Old Mac's have zoomed in price largely because foreign collectors, mostly Asian, grabbed all that they could get their hands on. They mainly listen through horn speakers. American audiophiles wanting the best sound are buying mostly modern amps, and they are the best deal if you get them in mint used condition like I did. My brother had a Counterpoint SA-100, and it blew away those old vintage tube amps as well. We had a listening session one night where I listened to several old vintage tube amps. The best amp we heard was a modern custom design using a 950V radio transmitter tube, but it wasn't cheap or small. Modern preamps show an even bigger leap in performance over the old vintage stuff. Now that I can sit on my butt and control my C-J PV-14L preamp, I will NEVER go back to anything vintage, for convenience as well as performance.
Convergent Audio Technology also makes a good amp and preamp. I have heard the CAT SL-1 preamp, and it had killer sound quality (at $4K it should have been good). The matching power amp is reputedly just as good. For my money, I will take my C-J amps over anything I ever heard. The dreaded listener fatigue is almost nonexistent with C-J amps. Some people prefer the Audio Research sound, and still others love Jeff Rowland or Pass Labs. My brother uses vintage Marantz. To each his own. It's like comparing Ampeg to Ashdown in bass amps. Some people do not want the highest fidelity amps, but prefer some euphonic colorations.
I can get a new or like new MV-60 for a little over $2K if I shop around, or $2795 full retail. However, for bass freaks I believe the solid state MF-2250 or MF-2300 would surpass. Old Mac's have zoomed in price largely because foreign collectors, mostly Asian, grabbed all that they could get their hands on. They mainly listen through horn speakers. American audiophiles wanting the best sound are buying mostly modern amps, and they are the best deal if you get them in mint used condition like I did. My brother had a Counterpoint SA-100, and it blew away those old vintage tube amps as well. We had a listening session one night where I listened to several old vintage tube amps. The best amp we heard was a modern custom design using a 950V radio transmitter tube, but it wasn't cheap or small. Modern preamps show an even bigger leap in performance over the old vintage stuff. Now that I can sit on my butt and control my C-J PV-14L preamp, I will NEVER go back to anything vintage, for convenience as well as performance.
Convergent Audio Technology also makes a good amp and preamp. I have heard the CAT SL-1 preamp, and it had killer sound quality (at $4K it should have been good). The matching power amp is reputedly just as good. For my money, I will take my C-J amps over anything I ever heard. The dreaded listener fatigue is almost nonexistent with C-J amps. Some people prefer the Audio Research sound, and still others love Jeff Rowland or Pass Labs. My brother uses vintage Marantz. To each his own. It's like comparing Ampeg to Ashdown in bass amps. Some people do not want the highest fidelity amps, but prefer some euphonic colorations.
-
toneman
Well.. seems like alot has happened in this post while I was gone...
First off, i would not use NOS filter/electrolytic caps in any amp as a replacement. My best source for new filter cans is CE Dist. which is the parent company of Antique Electronic supply in Tempe, Az. I've had excellent results using their cans(even though I've seen some bad press on these from other sites I think it's B.S.)
They also carry the newly manufactured Ei 12DW7's that are great as well.
Converting 6L6 to 6550 shouldn't be much as you can plug both tubes into the same wired socket. Usually, and it will work.. you can plug a 6550, EL-34, KT-88 into a socket that's been wired for 6L6 and it will work. However, I would make sure on an SVT that the socket is wired to what Ampeg originally wired them to if you're going to use the 6550's. Also, 6550's have a bit more output power than a 6L6.
If you can find the new Groove Tubes updated/new format Tube Book, it has all the Ampeg schematics in the book and also a CD-ROM with 400+ schematics.
BTW Phil; My 3 stereo's are oplf sixties Fisher's! A 100XB, 400 C & 800 B! I can't listen to CD's or LP's thru anything else!
First off, i would not use NOS filter/electrolytic caps in any amp as a replacement. My best source for new filter cans is CE Dist. which is the parent company of Antique Electronic supply in Tempe, Az. I've had excellent results using their cans(even though I've seen some bad press on these from other sites I think it's B.S.)
They also carry the newly manufactured Ei 12DW7's that are great as well.
Converting 6L6 to 6550 shouldn't be much as you can plug both tubes into the same wired socket. Usually, and it will work.. you can plug a 6550, EL-34, KT-88 into a socket that's been wired for 6L6 and it will work. However, I would make sure on an SVT that the socket is wired to what Ampeg originally wired them to if you're going to use the 6550's. Also, 6550's have a bit more output power than a 6L6.
If you can find the new Groove Tubes updated/new format Tube Book, it has all the Ampeg schematics in the book and also a CD-ROM with 400+ schematics.
BTW Phil; My 3 stereo's are oplf sixties Fisher's! A 100XB, 400 C & 800 B! I can't listen to CD's or LP's thru anything else!
Thanks Don,
I have a schematic but haven't checked the wiring yet, I am tempted to think that if any changes were made they were minimal at best because here in Lima they only do what they absolutely have to because people here don't want to pay for anything that is not absolutely necessary, so if I read you right then you are saying it is possible if the didn't rewire the tube sockets then I may be able to just plug in the 6550's and re bias them? (of course first checking for any wiring changes) You don't think they would have changed the bias voltage at all? I was told that stock this amp would melt the plates of 6L6's.
You know this amp originally took 6550's correct? and the plate voltage is somewhere around 650 volts. I don't know how a 6L6 can handle that much voltage unless they are running these tubes cold. A 6550 is capable of putting out 50 watts each, these heads put out three hundred watt RMS., the 6L6's are what about 37.5 watts maximum power?
I have a schematic but haven't checked the wiring yet, I am tempted to think that if any changes were made they were minimal at best because here in Lima they only do what they absolutely have to because people here don't want to pay for anything that is not absolutely necessary, so if I read you right then you are saying it is possible if the didn't rewire the tube sockets then I may be able to just plug in the 6550's and re bias them? (of course first checking for any wiring changes) You don't think they would have changed the bias voltage at all? I was told that stock this amp would melt the plates of 6L6's.
You know this amp originally took 6550's correct? and the plate voltage is somewhere around 650 volts. I don't know how a 6L6 can handle that much voltage unless they are running these tubes cold. A 6550 is capable of putting out 50 watts each, these heads put out three hundred watt RMS., the 6L6's are what about 37.5 watts maximum power?
Don, Fisher Radio was one of the greatest innovators in early audio design before the company was sold to Sanyo around 1970. I suppose you got your Fisher components before they became collectibles. I remember that one of their slogan's was "We invented high fidelity", which they probably had a right to say more than anybody else based on all their "firsts" in audio. I checked prices on eBay recently, and a lot of other people seem to think highly of Fisher also. Avery Fisher was to consumer audio amps what Leo Fender was to electric guitar amps. You know what happened after Sanyo bought the company. Cheap transistor designs replaced classic tube circuitry. My early 70's designed Fisher 190 receiver had "totem pole" output consisting of stacked NPN transistors that coupled to the speakers through electrolytic capacitors. Truly horrible sound was the result, with rolled off deep bass due to undersized couplng caps and a turn-on thump as the output caps charged up. Avery Fisher must have hated what Sanyo did to his company. A cold "solid state night" descended upon audio as early transistor designs replaced more expensive tube designs and old American audio companies died off due to cheap foreign transistor designs. McIntosh alone survived the 60's and 70's, only to also be later sold to the Japanese after other new American companies resurrected the American consumer electronic audio industry selling "high end" components. How musical instrument amp companies survived while consumer amp companies died in America would make an interesting study. It's not that American musicians have a lot more cash laying around for amps than the average consumer.