Estate sale find

[mojogoat]

Hi folks, new to forum, I scored a Rickenbacker black metal lunchbox amp at a local estate sale,$150, the condition is pristine as it looks like the amp sat in a closet for most of its life. Even the power cord looks great and the speaker looks fine. It arced under a tube and blew a fuse when I turned it on. My question is should I have it fixed or leave it original condition with all its old parts ? I have enough amps to play with already but I'm a little curious to hear this one.

[cjj]

Welcome to the RRF!


In my opinion, a non working amp isn't of much use. What most likely happened is that one of the filter caps in the power supply is shorted (the old ones tend to do this if they sit around with no power applied for decades). It's a pretty simple matter to find a suitable replacement, though they probably won't be in the big cans that were used way back when. For an original "look" you can often disconnect the can type cap (assuming that's what was used and is bad) and put a smaller, modern cap out of sight and get it working again.

I have no idea what that might do to "collector value" and, of course I'm totally guessing at what's wrong as well...

[doctorwho]

If the cosmetics are as excellent as you state, then I think (my opinion only) that it would be worth having an amp tech look it over and give you an estimate on getting the electronics working again.

[paologregorio]

This serves as a reminder; whenever one finds a cool old tube amp at a reasonable price, that's been sitting unplugged for years, don't turn it on-the caps have discharged and sending a full AC current through them is likely to blow a cap. Take the amp to a tech and have the tech charge up the caps with a variac. The $ you spend on this will more than save you the cost of a repair!

[mojogoat]

Thanks for the advice folks, I've been trying to find someone to work on it, local music repair place doesn't want to work on something this old but recommended a place that does vintage stuff, problem is, they don't return calls. Slim pickings for repair service here in Humboldt, Ca.

[Aclempoppi]

Hi,I'm also new to the forum, but not tube amps. Concur with you guys, amps that have set for some time need to be brought up slowly, with a variac or at least, a current limiter. You should be able to find a suitable filter can at:http://www.tubesandmore.com AKA, Antique Electronic Supply. Just a question, which tube socket arced? You might have dodged the bullet on the filter cap can and just taken out a cathode resistor, especially if it was the power tube. If I can bother you further, what model is this amp? Art

[mojogoat]

It was the rectifier tube, I just ordered all new caps,sprague atoms and Sozos. I'll try to replace them myself.

[paologregorio]

Toneman is in NorCal; he'll sort your amp out for you.

[Aclempoppi]

Right, a good tech might be the way to go! Rule # 1 is SAFETY!!! Mojo, If you want to take on the job, I would suggest you have the Spragues tested prior to installation. Their QC has been questionable over the past two years. The university's electronics department should be able to help you. We're talking about a two minute capacitance test, for all the electrolytics. And if you can form a relationship with someone in that department, it would be great if you can get the amp ramped up slowly, after your work. BTTW Mojo, you know, you have to check the voltages on both sides of that rectifier tube(AC on the PT side, DC on both plate output's side) . A blown fuse usually points to a B+ power supply failure. If you don't know what I'm talking about, don't mess with your amp. Rule # 1 is SAFETY!!!! JMHO, Art

[mojogoat]

Thanks for the advice, As for repair shop, seems no one I can find in humboldt wants to work on something this old. I could drive to SF or Sacramento but its 12hrs round trip. I found a broken wire from the transformer to a cap. Arcing under the rectifier tube left carbon on it so I order another one. I also found a paper cap that was staring to melt. I'm ordering a Variac . I've been reading allot about amps and amp repair, I ca read the schematics now and when I feel confident enough I will start testing and replacing. The internet seems to deliver unlimited information. I have 3 other tube amps and a hammond organ, I have always repaired everything I own with the exception of electronics. I'm retired and have the time now to learn.

[Aclempoppi]

Sounds like you're taking the right path, Mojo! There are plenty of good books, on the amp repair subject. 25yrs ago, I started with the Naval Manual on Basic Electronics, a 1960's edition(from the library). Have fun!!! You might want look into how to discharge the filter caps, on the internet, right away. It's a simple procedure and a must, if you get your hands inside the chassis. BTTW I started ordering F&T filter caps about a year ago, before that I always used the Sprague Atoms. But as long as you test each component prior to installation, whatever you choose is great! Art

[Aclempoppi]

Some resources, Mojo. http://www.aikenamps.com/techinfo.htm;. ... ntflow.htm As far as books,I'd consider- Kevin O'Connor and Tino Zottola as reputable and understandable authors, for a start-up. Can't seem to get this to work correctly! But you should be able to get the info. HTH Art

[mojogoat]

Thanks for the info! I enlisted in the navy in the early 70's and was scheduled to go to Electronics technician school until I failed the color test, couldn't see a shade of blue, ended up a machinist mate. I already ordered a resister to make the cap discharger, also a cap tester. I am a tool junkie so now I have a reason to procure more equipment. I always have the right tools on hand for a job before I start work. Again thanks for the info and support.

[mojogoat]

What else do I need to set up my tube amp repair bench? I have recently purchased a variac, tube tester, and a cap tester, I have a multimeter and digital soldering iron.

[AndyM]

what else for test bench? an oscilloscope and audio signal generator would round out your existing test gear. It doesn't have to be capable of measuring and analyzing MegaHerz.
Another option is to build yourself a dummy resistive load. Decide on the maximum wattage you might anticipate - up to 100 Watts for a guitar amp, higher for some bass amps. Ensure there's cooling and have a switch for 4 and 8 Ohms, input and output jacks (to measure ac signal voltage) and jacks to connect a digital voltmeter. This box in conjunction with a signal generator and scope can verify amplifier output wattage and run the amp at high power without waking the neighbours - since the speaker(s) won't be in the circuit.