crate 1r reverb repair

[action_jxn]

Hello humans! First time, long time, can't believe I got through....

I'm in the early stages of learning how to troubleshoot electronics. I'm currently enrolled in a training program to become a Biomedical Equipment Technician. However, I think fixing this old amp might be more difficult than some medical equipment.

I decided to work backwards from the potentiometer and found that, almost certainly, a resistor was missing, causing there to be an open circuit in the reverb section of the amp. This would explain why it doesn't do anything! However, I can't find a schematic online for the amp, and I'm not sure what the value of the resistor should be. How would you all go about working on this?

Also, I know these early crate amps stink. I have to use a boost pedal to make it sound almost ok, but it's quiet and looks cool. Also, it's so rudimentary that learning how it works seems like a good learning experience.

Thanks for any and all advice!

[The Dude]

There's a schematic here, but supposedly with errors. However, it might help with resistor identification and troubleshooting, anyway.

https://music-electronics-forum.com/...1&d=1503924711

[action_jxn]

I think the issue is on the input/Vcc side of the pot, but I'm having a difficult time figuring it out from the schematic. It's the very first component attached to the input lead of the potentiometer...

[action_jxn]

There's a schematic here, but supposedly with errors. However, it might help with resistor identification and troubleshooting, anyway.

https://music-electronics-forum.com/...1&d=1503924711

Thanks, I think it's making me more confused, but I was able to nail down where the issue is, just not what component is missing.

[The Dude]

....It's the very first component attached to the input lead of the potentiometer...

Are you talking about C20- between emitter of Q9 and the reverb level pot? If so, it's shown as a 1uF cap.

[J M Fahey]

Hello humans! First time, long time, can't believe I got through....

I'm in the early stages of learning how to troubleshoot electronics. I'm currently enrolled in a training program to become a Biomedical Equipment Technician. However, I think fixing this old amp might be more difficult than some medical equipment.

I decided to work backwards from the potentiometer and found that, almost certainly, a resistor was missing, causing there to be an open circuit in the reverb section of the amp. This would explain why it doesn't do anything! However, I can't find a schematic online for the amp, and I'm not sure what the value of the resistor should be. How would you all go about working on this?

Also, I know these early crate amps stink. I have to use a boost pedal to make it sound almost ok, but it's quiet and looks cool. Also, it's so rudimentary that learning how it works seems like a good learning experience.

Thanks for any and all advice!

Welcome to the Forum and to the Tech Profession.

You can *build* and amp without theory, just "painting by the numbers"and many do, successfully.

You usually have a PCB, a layout , a parts list , many times not even a schematic, just insert parts where asked, solder wires, jacks and pots faithfully as instructed, and you most probably build a working amp or pedal.



As you see, every* part, wire, pot, switch, connection transformer, etc. is clearly marked.
You build it, then check every single connection.
If yours matches layout, it "must" work.

NOW, repairing a ready built amp, with an unknown problem, is *absolutely* different.

Here you must know theory or its practical application, be able to measure and do Math, compare measured value with whatīs expected (which you "should" know beforehand or worse, be able to calculate or estimate on your own) ... a very different game.

This first step takes at least a year.

[Mars Amp Repair]

Hello Action_JXN,
I'm not completely clear on the symptom: Here are a couple of tests that can roughly give you an idea of which section of the reverb circuit is not functioning. NOTE: this is only if you have no other form of testing.
1) If you disconnect the output side of the reverb tank RCA cable & buzz the end of the RCA plug with your finger, do you hear the buzz thru the speakers?
2) If so, the reverb recovery part of the ckt is working (Q8-Q9 from the schemo linked in prev post). Not a definite, but a rough way of testing.
3) If it buzzes, then you can roughly check the send circuit (Q6 & Q7) by disconnecting both RCA cables from the reverb section & quickly touch them together. If the drive section of the reverb circuit is working, you should get a really loud/nasty squeal.
Hopefully, this will help to locate the circuit at fault.
I am also assuming you have tested the resistance of the tank. Most transistor/opamp driven tanks have relatively high resistances as compared to the tube driven ones. In this case if the tank is the original, you can be pretty sure it's ok if you just have resistances between 200 & say 2K.
Hopefully, this helps. glen

[g1]

I decided to work backwards from the potentiometer and found that, almost certainly, a resistor was missing, causing there to be an open circuit in the reverb section of the amp.

Further details as to why you came to this conclusion would be helpful. Where did you find an open circuit and how did you verify it?

[J M Fahey]

If it can help, Crate C1R or CR25 or something like that, their very first amp, the one housed in unfinished pine boards, was a shameless copy of a then very popular Peavey amp: 20-25W RMS, single channel, reverb, no tremolo, so close that the Peavey schematic can be used to service the Crate.
Maybe some parts numbers do not match, no big deal.
Donīt remember the Peavey model by heart, Enzo certainly did, if somebody remembers it, please post it here.
It was Peavey entry/practice model in the early 70s.