Fender DRRI Reverb Problem

[industrialarts]

I have an interesting problem with Fender Deluxe Reverb Reissue reverb.

The amp came to me with no tank so I put the recommended 4AB3C1B tank in and it sounded awful, the reverb was overdriven and distorted. I put a 400Hz sine into the amp, looked at the input to the reverb transformer and it had a weirdly distorted signal, there was an additional peak and a flat spot. I checked all voltage, ac and dc and they all match the schemo.

Here is everything I swapped out - tried another thank, different cables, 12AT7 tube and the reverb driver transfomer. Checked for wrong components in reverb driver circuit, all match schemo.

In trying to find the problem source (circuit, tank, something else) I tried 4EB3C1B, which is used in the Fender Hot Rod series, which use an opamp to drive the tank. With this tank it works fine, no distortion. I then tested with a 4FB3C1B which also worked but the reverb gain was low (which I expected). As I'm sure many of you know, the only difference between the tanks is the input impedance.
A = 8 ohm
E = 600 ohm
F = 1475 ohm

Just for the record, I have fixed dozens of reverb circuits, replaced thanks, troubleshot many a weird problem, this one has me guessing. I have a suspicion it may be the filter caps - they are the IC caps and these often fail in Fender amps - but they look clean, no sign of leakage. My solution will be to use the 4EB3C1B if I can't find another solution.

Thanks!

https://www.ampwares.com/schematics/65_Deluxe_Reverb_RI.pdf

 

[Whoops]

You should post in this forum as it's dedicated to Tube Guitar amps a lot of experienced and helpful people around there:

https://el34world.com/Forum/index.php?PHPSESSID=lpn728141a3sq1sj836gbkknd4&board=13.0

 

[Tubetec]

Ive tried subbing in a few different tanks with different drive /recovery stages , amps with low imp tube/transformer drive still work quite well with higher imp tanks designed for op amp drive , theres a little less 'shake,rattle and roll ' from the springs but you still have plenty of gain in the recovery stage to make the sound as wet as you like . Be aware also of tank orientation , if the tank is set up in the wrong plane the magnetic slugs rub off the lams and create a horrible grainy distorted sound. Simply tapping the tank sharply should be enough to tell you if the springs are floating freely or not .

 

[industrialarts]

Thanks for the tips - I left the 4EB3C1B tank in, it was more than 'wet' enough. I use MOD tanks all the time now, I think they sound better, smoother and not quite so 'boingy' as other tanks, but TEHO