Hello and DIY Amp Identification Help Please

Topjimmy74

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Hello everyone. Long time lurker first time poster. I've been getting more and more into tube amps. Going to be building a RobRob Deluxe very shortly. Along the way of learning, and some inherent GAS, on that project, I ended up purchasing an amp that was built by a local EE sometime around 1990 from what I understand. I don't know anything more about its history. I'm wondering if any of the gurus here can identify the type of circuit it's based upon by reviewing the three attached photos. Apologies if this is a silly question; I'm new and learning, but not knowledgeable enough to figure this one out at the moment. The OT is a Stancor A-3311 if that helps. The amp works as is, based on very limited testing shown to me by the seller. I intend to replace the plug (adding a ground), input and output connections and the caps in the near term, but probably not much else (unless you have any great ideas ;). I'm perplexed by some of the chassis grounding. Anyway, it's a joy to look and learn with these amps. Any helpful tour guide services you can provide are greatly appreciated! And also, yes, I understand the safety considerations involved in working on these even though I'm new. Thank you all for your time and any help.

All the best,
Leo
 

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Snfoilhat

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One great way to learn this topic would be to study the amp you have in your hands.

Write down what tubes it uses, and that alone is a big clue to what circuit it may be based on. Note whether the rectification is solid state or tube. That isn't the best clue, because so many builders have changed one to the other, but it adds to the picture. Write down what the controls say or (if they are unlabeled) do, once the amp runs. The control set is probably the next most useful piece of info. Lastly, since this amp is relatively simple and wired in a style that lets you see all the connections, I would get some paper and draw it out. You won't know all the schematic drawing conventions and shortcuts yet, but you should be able to get a decent sketch of how things connect, and then you'll be able to do all this stuff yourself, or ask for help in a way that others can easily interpret. Good luck!
 

Topjimmy74

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Thank you, yes, that's on the slate for this weekend or next. Just haven't had time to dig in yet and chomping at the bit for my insight.
 

Wally

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So, you have a 5U4, 2 x 6V6s, a 12AX7, and a 6AU6, correct? Is that RCA Jack the only input? This would be a good learning platform. Learn about tubes…what are the elements and what do they do?? Search ‘history of vacuum tubes’. There is a Wikipedia article that will take you through the basics In layman’s terms. Learn about safety measures. If that RCA Jack is the only input, you may have an amp that was intended for something other than a guitar. Where does that yellow wire from that RCA input Jack go? As @Snfoilhat says, one would have to trace that circuit out to understand what goes on.
 

W.L.Weller

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The non-12AX7 preamp tube could also be a 6AV6. Based on the OT & RCA jack, I'd guess that this is a mono amplifier intended for use with pre-recorded sound sources. Whether it's intended to accept a line level signal or includes a phono stage with the necessary amplification and RIAA equalization would require some study of the circuit.

Here's some folks talking about that OT in the context of home audio reproduction:

 

Topjimmy74

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Thank you all very much. I'm going to see if I can pull together a schematic. That, in and of itself, will likely be quite a feat for me, but certainly worthwhile. I appreciate your time and input.
 

Topjimmy74

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Started rough mapping things out. I'm sure this is horrendous, but I enjoyed doing it. Traced it through the three pots; enough for tonight. Thanks again for the help today.
 

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