Sunn Model T

winston · Post by **winston** » Sun Oct 23, 2005 11:53 am

Charlie,

I have a Sunn Model T head c/w a Sunn 610 Bottom that I purchased new in 1975. I have never had any work performed on this amp at all and it still sounds and play like it did back then.

What is your opinion of how well or conversely how poorly these amps were constructed. Also your opinion on the speaker cab design and the speakers used.

I have used mine in all types of situations from large 21,000 seat venues to 200 seat venues. I usually use it in conjunction with my Les Paul. If I use different settings my 360/12 also sounds very nice through it.

Is it unusual for a Sunn amp to last this long or are they all as robust as mine has been?

soundmasterg · Post by **soundmasterg** » Sun Oct 23, 2005 3:37 pm

Sunn made some really fine products, and just about all of them are very robust and long lasting. A lot of them were based on Dynaco hi-fi stuff, and used the excellant Dynaco transformers also.

That said, if you haven't yet, you should replace all of the electrolytic caps in the amp. Electrolytic caps have a definite lifespan and when they fail, they can take things like your power transformer with them. I'm not sure if your amp has a can cap or not, but with today's wall voltages being higher than they were back when you bought that, a replacement can cap will probably have its voltage rating exceeded by the voltages in the amp. The best way around this, and actually a cheaper way than using a can cap, is to use discrete caps wired in series. If you use 2 350v caps in series, then you get a 700 volt rating at half the microfarad value on the cap, which will exceed the likely plate voltage of at least 550v, and will exceed the can cap rating of 525v. When you wire a pair of caps in series, you also need a 220k 1w resistor in parallel with each cap. You should use series connected caps for at least the first two filter cap sections in the amp, and perhaps the third one also, depending on where the voltage is. If you don't understand any of what I just said, then take it to a tech to do the work. Tube amps can kill you if you don't follow proper safety rules when working around high voltage.

I have a 1968 Sunn 2000S that I haven't overhauled yet and it still works fine, but I did overhaul and modify a 1970 Sunn 200S with larger filter cap values, and it sounds a LOT better than the 2000S, largely because of the new and bigger value caps. I use it for bass though, so the larger caps are a benefit. If used for guitar, the values you have stock would be fine.

I would guess that the speakers in your Sunn cabinet are made by Eminence.

If you have the electrolytic caps replaced, then your amp should last for another thirty years easily. The coupling caps should also be checked for leakage and replaced if they are leaking badly too, but that isn't as critical as the electrolytic caps being replaced. Sunn used a lot of green Cornell-Dublier paper caps, and they're pretty ****** caps. Any film cap today would be better than those, although it would sound slightly different if they are changed.

winston · Post by **winston** » Sun Oct 23, 2005 5:31 pm

Greg,

Thank you for going into such detail. One question for you. You mention that if I change the green Cornell-Dublier paper caps with film caps that they would alter the sound of the amp. Can you describe what sort of change to the sound I could I expect to hear. Will the film caps for example provide more of a mid range boost, roll off the highs or ?

Thanks again for taking the time to assist.

soundmasterg · Post by **soundmasterg** » Sun Oct 23, 2005 6:09 pm

Well any paper cap rolls off the highs to a certain extent compared to a modern film cap. Overall the paper cap sounds smoother, although it is a subtle thing. The problem with paper caps is that they dry up just like old electrolytics and need to be replaced eventually, because they can leak DC volts to the next stage and throw off the bias of that next stage. Not all the coupling caps in your amp would be paper...some of the brown ones might be polyester, though they weren't all that great of quality as compared to modern caps either.

The best replacements in my opinion to sound closest to the original would be the Mallory 150 series. There are many other types that you could use that work work well and sound good also, such as Orange Drops 716P, or the Orange Drop PS series, or the Antique Electronics yellow polyester caps, or Sozo caps. You can use them to shape the sound in a subtle way, kind of like changing to different brands of tubes.

What I would suggest is to get all the electrolytic caps replaced first, and make sure the amp is working well after that, and then go ahead and test the coupling caps for leakage, and replace as necessary. Just make sure with the electrolytics to use individual caps wired in series with a parallel resistor so you will get a high enough voltage rating.

On my Sunn 200S, I just replaced everything in it as the first couple caps I checked were leaking, and some resistors were bad too. I use mine for bass, so I went with different caps than I would use if I was using one for guitar.

winston · Post by **winston** » Sun Oct 23, 2005 6:51 pm

Greg,

Many thanks for the info. We have a local amp tech here in our little city that will be getting a print out of this info along with my head so it can be brought up to snuff.

soundmasterg · Post by **soundmasterg** » Mon Oct 24, 2005 12:16 am

Glad to help Brian. If you need more help on it, let me know.

triode · Post by **triode** » Sat Oct 29, 2005 10:34 am

I agree with Greg. The Mallory 150 Series are real nice, mellow, not tubby and veiled, like Orange Drops can be. BTW, there are at least a dozen different varieties of orange drops. Different construction types, materials used,etc.