CONVERTING 110V AMPS TO 220V OPERATION

[Dougdh]

Hello, my name is Doug and I greet you from a fairly cold Johannesburg, South Africa (11 degrees centigrade).

The Hoffman amp site is extensive and it's a privilege to be amongst knowledgeable gents such as yourselves.

I've been involved in converting a number of 110V valve amps to 220V operation and have had success.

However, I have run into a problem which I have not been able to find info about.
The amp is a Fender Twin Reverb II, circa 1984.
The original 110V transformer:
Primary 110V.
Secondary  320-0-320 centre tap (CT).
A separate winding of 60V for bias, and a separate winding of 6.5V for heaters.
The 220V transformer:
Primary 220V.
Secondary 320-0-320 (CT),
part of that winding is a 60V tap for bias
and there is a separate winding of 6,5V for heaters.

The 110V transformer had one end of its bias winding grounded.
The other end was connected to a resistor-diode-smoothing cap for bias.
The HT winding went to a 4-diode bridge rectifier, with its negative to ground.
The HT centre tap went to the junction of two caps with resistors across them.
The full HT is from the top cap to ground.
The 110V transformer centre tap appears to be floating.

With the 220V transformer, this arrangement doesn't work.

The 110V circuit schematic makes the above clear.

Do you have any suggestions of how to solve this problem?

Kindest regards,
Doug
(FIRST TIME POST)

[EL34]

Welcome to the Hoffman Amps forum

There are many different boards on this forum for different topics.

The Tube Amp Building - Tweaks - Repairs board is where you can post amp questions.

That board is listed here.
https://el34world.com/Forum/index.php?board=13.0

Thanks,
Doug Hoffman

[EL34]

You are posting in the wrong board

See the message above

Copy and paste your question to the board listed above

[Dougdh]

Thank you. Have reposted