Discussion - #102 Robben Ford Amp (High Plate Skyline)

[samtech60]

Building a 102 from scratch I have a beefy power transformer reading bout 398 vac no load . It has about 7 amps for heaters and a negative bias supply winding of 60volts so should we be good shape ?

Or will I have to make power supply adjustments for being about 50 volts higher than normal for the high voltage secondary voltage?

This was originally in a crate turbo valve 60 amp made in America back in the 90s ? It was designed for a 60watt amplifier . Just curious how it would sound with the higher than normal plate voltages of about 50 volts ? Any input would be appreciated

[martin manning]

You can increase the first dropping resistor after the choke to bring the preamp voltages back in line. A member here built an ODS with 500 V on the power tube plates using a Peavey PT and was very happy with it.

[bepone]

Building a 102 from scratch I have a beefy power transformer reading bout 398 vac no load . It has about 7 amps for heaters and a negative bias supply winding of 60volts so should we be good shape ?

Or will I have to make power supply adjustments for being about 50 volts higher than normal for the high voltage secondary voltage?

This was originally in a crate turbo valve 60 amp made in America back in the 90s ? It was designed for a 60watt amplifier . Just curious how it would sound with the higher than normal plate voltages of about 50 volts ? Any input would be appreciated

this transformer is not good for modern use, for several reasons. still can be used with "modifying" the power supply in several ways.

398VAC B+ voltage will be too high after rectification, will be around 530V DC. Ug2 which is more critical , will be cca 520VDC.

Ug2 over 500V is not healthy at all for moder tubes, they will arc and flash inside depending on the quality (random , and not comparable to old tubes)

old 6L6 GC (Sylvania etc) can withstand this voltage, also 7027 like seen in old Ampegs (V4).. modern 6L6GC ot EL34 absolutely cannot work on those voltages reliably.

this transformer can be used , if is used with additional power transformer (lets say 270-300VAC) which will supply ONLY screen g2 voltages , and maybe preamp too, and main transformer will supply only anodes.

or this transformer can be used with another 40VAC 30W transformer in "bucking" configuration , where 40V will be DEDUCED from 398V, and then A and g2 circuits will be supplied from "more normal" 470VDC.

[samtech60]

Screenshot_20230806_214517_Gallery.jpg

[samtech60]

This particular amplifier was rated at 60 watts pushing either a pair of 6L6s or optional EL34s

[pompeiisneaks]

Moved thread to discussion, please remember to not post 'discussion' details in the files section. We want that to retain only the file content as much as possible.

~Phil

[samtech60]

Understand thanks