blues jr no reverb

[Papa Jim]

previous post fixed friends blues jr from redplating works great except no reverb. Followed all BillM's troubleshooting it and all good. Last thing was replaced the opamp driver. No fix. Schematic say's to measure TP's I need a 10mv 1khz input signal to amp. My old hp signal generator not going any lower in frequency than this. Will this hurt an amp. The pk to pk is ok.
500uS per div scope setting with one cycle taking 5 divisions. Would that be 1/25ns

[sluckey]

That's a nasty looking 400Hz sine wave.

[Papa Jim]

Yeah, the old oscillator is tube from the 50's. I think I will just rob the parts out of it instead or build an amp inside of it. Lol  For now I will just strum my guitar or buy a little 10 dollar oscillator off amazon.

[sluckey]

400Hz is lower than 1KHz.

[Papa Jim]

Yes I know. So is the nasty signal ok. I just looked and the oscillator is missing a el86 tube. That may be why the knob for the frequency control is not working.

[Papa Jim]

I meant I know now that you pointed it out. I was off on my decimal points. Thanks. I will give it a shot.

[shooter]

a "test" signal should be representing something useful for your needs, a guitar amp ~ 80hz - 5khz, any amplitude that you would expect to find from a real source, so small milli's to small volts.  5gig @ 1kv is probably not helpful 

[Papa Jim]

That makes sense why the blues jr schematic say's all the test point voltages are measured with 10mv rms at 1khz input. Although the vernier dial for frequency on my oscillator doesn't work I have a multiplier x rotary step switch that does happen to change the frequency. I think it will be sufficient now to use it for troubleshooting thru the reverb circuit vs using my actual guitar signal.

[sluckey]

400Hz will work just fine. The 10mV is more critical.

[Papa Jim]

Well I went back and can't get the amplitude down now below 1v (probably need to get the missing el886) so just said heck with it and used my guitar. Good signal on scope into the tank
at the internal tank input rca when connected up to tank but nothing out of tank output side. I get a hum that I can make the volume change by turning the reverb pot if I unplug the output tank wire and grab the center conductor on the rca plug. This means the opamp is good. New tank time?

[PRR]

What is the resistance looking into each end of the tank?

[Papa Jim]

last week when I started looking into fixing it by the billm instructions the input side at the connector of the tank when disconnected from the amp was 58 ohm and the output side was 236 ohm. This morning they are both infinity. I don't know what happened unless hooking a tank up backwards will blow it. I had some confusion one time about the in and out due to discrepancy of how it was connected when I received the amp vs how it is supposed to be were opposite. Suspected a connector problem so slid it off and measured at the transducer pins with same result. I have only hooked this tank up to this amp only and absolutely nothing else. I promise. To me it is unreal that both sides would be blown. 

[PRR]

> unreal that both sides would be blown. 

Yes. I suspect a measurement mistake. Check a stray resistor and see if your meter works.

No, backwards won't blow a tank. Just weak reverb signal until corrected.

[Papa Jim]

re-checked with same result open result. Checked my measurement technique by a using another tank sitting beside this one that measured 225 ohms on output and 1.3 ohm input.

[Papa Jim]

So I said what the heck nothing to lose trying to repair. So it turns out one of the transducer wires bad at the solder joint to the pin. Found by breaking it loose, undoing one wrap. Remove the varnish for a continuity test that is 60 ohms now. If successful soldering it should be good to go. Kinda like working on a pickup and as long as the other break is not deep withing the coil I might be able to salvage this tank. I have to apologize because there is a possibility due to some disabilities I have one of them short term memory, among several others that I could have been mistaken about previously getting measurements on this tank. It could have well been the other tank only. Sorry about that Sluckey, Shooter, and PRR.

[jjasilli]

Good job! But, I won't work on such amps anymore.  Find it; fix it; and next week some other fault.   

[Papa Jim]

Well I fixed the input transducer and got 60 ohms, but the output transducer after taking off several winds I can't find the break so giving up on it and the friend is just gonna have to pay for a new one. I've been  on this when I should be working on my AB763 Deluxe Lite amp.

[Papa Jim]

Okay so the new tank and a new op-amp fixed it up it is working great now.