Hey everyone!

My setup is: Fender Jaguar American Professional Standard, Twin Reverb ('72), reissue Fender tank. The amp on its own is crazy bright (it's the model with the pull bright boost on the master). When I bring the tank into the mix, it's TOTAL brightness killer... it's as if I've rolled almost all the treble off about 50-60%. To compensate, I've had to get an EQ pedal to help bring back some of the lost highs. I don't get what's happening... New tubes in both the Twin and the tank.

Can anyone shed any light on this? Shouldn't my tone with only the tank put before the amp be bright? I can't understand why I'm losing high-end...

The Men in Gray Suits (Montreal, Canada)
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synchro wrote:

That is strange. Have you tried the tank with another amp? Almost certainly, the effect would be the same, but it’s a good data point to add. The next thing I would try would be to put the Mix to having the reverb as high as it would go and see if the problem persists with the bypass circuit essentially out of the mix, and while you are in this mode, try various settings on the Tone control to verify that it is working properly. The tone pot would be an obvious suspect, but it should have an effect on the wet signal, only.

One very simple test would be to try putting the mix control at the other extreme and see if you are getting losses on the dry signal side. Another test would be to use the foot switch to put the tank in bypass and see if you are still getting the same reduction in highs.

The ideas above would help you to, possibly, narrow down the list of suspects. The signal going into the unit is split into two paths, the wet reverb side and the dry, non-reverb side. As I mentioned before, the first suspect would be that the tone pot has failed, allowing too much of the signal to hit C9, and the unit would essentially act like the tone was turned all the way down, all the time. If the brightness returns when the Mix is set to full dry, that would point another finger at the Tone pot.

There are other places that trouble could creep into the picture, but from reading the schematic, it’s unlikely that the unit would function. Loss of highs implies that highs are being shunted to ground somewhere, and there are only a handful of caps that have one end connected to ground. If there was a problem in the cathode circuit for any of the tubes, I doubt that the unit would work at all.

Keep in mind that the filter caps in the power supply store a high voltage charge, even when the unit is off and unplugged, so I wouldn’t recommend poking around in the chassis unless you know how to discharge those caps, safely.

Please keep us posted.

I tried it with my Quilter Pro Block 200 and had pretty much the same results (the TB's tone settings aren't your typical bass/treble, so it's probably not a great one to test on). It was suggested that I stop using cheap patch chords (guilty, sigh), but for the fact that when I bypass the tank altogether, it's much brighter. The tone control seemingly works well because I do hear a difference when it's maxed out or not... but at full, it still sounds like it's blanketed, tone-wise.
I'll check it out on another amp this weekend... thanks for the input!

The Men in Gray Suits (Montreal, Canada)
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Seems like an issue with the tank, I use a Surfybear into a Deluxe Reverb and the highs are pretty definitely more pronounced with the tank in the chain.

Wellens_ wrote:

Are all of the caps right?
Good tubes?
Cheers, Andy

Yes, the tubes are all new. My next stop will be the caps, I'm thinking.

The Men in Gray Suits (Montreal, Canada)
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edwardsand wrote:

Also you might check the connections to the reverb pan and make sure they are not loose. Another issue can be the pan - check to make sure it's the right model (4AB****) and you could change out the pan to see if the current one is faulty.

That’s a good point. An impedance mismatch for the pan could make for all sorts of fun and games. One thing for sure, use good quality reverb cables. Bad reverb cables can make you wish you were never born.

The artist formerly known as: Synchro

When Surf Guitar is outlawed only outlaws will play Surf Guitar.

kick_the_reverb wrote:

Just pointing out that the "bypass pedal" in a reverb unit is not a bypass pedal at all. To test "dry" signal through the unit, I recommend turning both mix and dwell to zero.

Ran

Agreed. My choice of words leaves room for improvement. It’s not bypass, in tne sense of the bypass in a stomp box. More correctly, the input splits between wet and dry signals. The footswitch prevents the reverb from functioning, but the signal is still routed to both the wet and dry signal paths.

I’m quite curious as to how this will all sort out. One thought that occurred to me is that if the input impedance was too low, that would tend to cut the highs. One easy test would be to put a buffered bypass pedal in front of it with a short cable between the pedal and the reverb unit. If this improves matters, that would make me suspect R1, V1, or the circuit components related to V1, perhaps R4 and/or C2.

The artist formerly known as: Synchro

When Surf Guitar is outlawed only outlaws will play Surf Guitar.