Click to enlargeDOWNLOAD 1957 Twin Reissue improvements and fix - cool new stuff!

57 twin web page This is one in Fender's line of hand-wired “boutique like” amps. A reproduction of the 1957 Twin amp.

 We had heard from our friends and customers of mixed views on this amp. Some said it was fabulous, but others noted some disconcerting problems with it.

 Gustavo P. got one recently and after putting in a Torres Premium Select '57 Twin Tube set (to replace the bad tubes the amp came with) he still had the lingering problem.

Gustavo sent me a very high resolution MP3 of him playing the amp (thanks by the way) and the fuzzy crossover distortion others had noted was right there.

 Sounded like a blown speaker, a fuzz on the edge of the notes.

After trying some troubleshooting via email we decided to get the amp into the shop so I could take a look at it.

Right away it was evident what was wrong. Even testing with regular 6L6 tubes the amp could not be biased – with the beautiful KT66 tubes we were using, the problem was even worse.

The bias supply would not provide enough negative voltage to bias the tubes into the correct current draw.

After applying the normal fixes, and doing some repairs (a bad bias pot too) a check of the AC showed that the bias tap on the power transformer did not provide enough raw AC to get the correct negative DC Bias to make this amp work right.

Rather then build a whole new bias supply into the amp (always a possibility) I applied a new design voltage doubler to the negative voltage supply.

A fabulous new Torres technology. Now I had DOUBLE the negative voltage, plenty to push the KT66 tubes into the correct AB range – Problem solved.

It sounded immensely better, the fuzzy tone was virtually gone – very good, but it wasn't ALL gone.

There was a little hint of crossover left, audible when the amp was set up very clean with very close listening.

It was probably inherent to the amp's design. Where was it coming from? A study of the schematic found it – an unbalanced phase inverter.

It has exactly the same Concertina phase inverter as a Princeton Reverb, and has exactly the same unbalance error, so my long-ago modification design, the "Perfect Prince" is included to correct this pre-existing error (and existing in ALL  the amps I have ever seen with the split load, concertina phase inverter of this design) - it corrects the problem, well, "perfectly".

The Download includes all the instructions for both these mods, plus has a parts list for all the parts. the Highly accurate resistors are available from - AND the mod includes a needed capacitor upgrade for the signal caps.

Overall a great project for less then two bucks.

Your download will appear as a DOWNLOAD button on the order confirmation page. You can also get to it, even from another computer from the ORDER STATUS PAGE. if you have trouble, please contact us with your order # and we will send you a copy

DO7573 download$1.95
Download all instructions and parts list: 

Click to enlargeParts Kit for th '57 Twin fix/mod/upgrade Parts Kit for the '57 Twin Modifications and bias repair.

You need to download the instructions they are not included with the parts kit.

The parts kit includes the new diodes,
filter caps for the power supply,

all the parts for the Driver/Phase inverter fix including matched Caps for the driver.

AND all the signal caps to upgrade the circuit board.

Parts Kit for th '57 Twin fix/mod/upgrade
Gu7574 57 twin$75.95

final notes on web page

Dan's Legendary Book "Inside Tube Amps" is now available on Amazon/Kindle

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Torres Engineering

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Yuba City CA 95993

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in business 48 years