Deluxe Reverb Clone too "throaty"

[keithpop]

Hi All,
I just finished building a Deluxe Reverb clone. The Normal channel is perfect for me. It begins to break up around 5. Sounds very full with great harmonics.

The problem is the "vibrato" channel. It sounds very throaty (if that is a good way to describe it). It also starts to break up around 3 to 3 1/2.

I have swapped V1 and V2 preamp tubes and it doesn't change anything. I am using NOS Telefunken 12AX7's. I have ruled out the speaker because one channel sounds so good.

Any hints why I would have such a difference between the 2 channels and any suggestions on how to calm down the vibrato channel?

Thanks for any suggestions.

kp

 

[mario13]

Hi there,
I would check the tone stack of the vibrato channel first to rule out any accidentall miss wirring.
Mario.

 

[keithpop]

Thanks Mario. I will check it again. Before I plugged it in the first time I triple (and some places quadruple) checked the circuit. I will also look at the components used in the vibrato channel. I used a lot of NOS capacitors (40-50 years old) in the normal channel and mostly new orange drop capacitors in the vibrato channel. I ran out of my supply of NOS .1 mF and .047mF capacitors so had to buy new from Antique radio Supply. I am not sure how much this would effect the throaty sound or early break up. Thanks again for the suggestion.

 

[mario13]

Hi again,
Since you mentioned the caps ( i gather your refering to coupling caps between stages) it wouldn't hurt to test the ones on the vibrato channell for DC leekage. This would have the effect of throughing the bias of the next stage off, resulting in distirtion sometimes. Also check your voltages on your preamp tubes make sure they check out ok.
Mario.

 

[rongon]

keithpop,

If all voltages, parts check out OK...

You mentioned that the Normal channel breaks up at vol ctrl setting of 5, while Vibrato channel breaks up with vol ctrl at 3.5. That doesn't sound abnormal.

The Vibrato channel on a Deluxe Reverb is normally quite sensitive. It has an extra 1/2 of a 12AX7 in the signal path, so noticeably higher gain than the Normal channel. It's part of the design of all silverface or blackface Fender amps with reverb. The Deluxe, with its 6V6 output tubes, is easier to bring to full power than the bigger amps (Bandmaster, Tremolux, etc.), so distorts quickest of the these amps.

--

 

[jjman]

Also should swap V1 with V4 since V4 is in the Vib channel's circuit. Just in case.

 

[keithpop]

Thanks all for the input.

I am going to continue to look at the coupling capacitors in the vibrato channel. I spent a couple of hours swapping tubes today and ended up using RCA tubes in place of the Telefunkens in V1 and V2. I also had better results replacing the RCA 6V6 tubes with old TungSol tubes and I increased the bias current from 21 mA to 23.5. All voltages are within reason (plus or minus a volt or 2). It no longer has the "throaty" sound but the vibrato channel does distort much sooner than the normal channel. It has been 35 years since I owned and played through a deluxe reverb amp. It's a good point that the vibrato channel would be more sensitive than the normal channel. It certainly has more to do.... It is also much louder than I remember. I guess I still get to annoy my neighbors.

If y'all can think of anything else....please pass it along.

Thank you all very much for the input.

keith

 

[keithpop]

Aha! For anyone who cares.... I found my issue with distortion in the vibrato channel. It's hard to admit but I know my eyesight is not what it used to be. I installed a .0033 mF capacitor in the tone stack instead of the .03 mF the schematic required (I built the '63 circuit). Off by a factor of 10....no wonder it sounded lousy.

I installed a very old Cornell Dubilir .02 (I have lots of those) and the amp now sings like it's supposed to sing. I also installed the same capacitor in the Normal channel to replace the .033 mF I correctly installed....just for balance. Works great.

Again thanks to everyone for assisting me with this problem.

keith