DeArmond (Rowe) Guitar Amplifier Model R25T Restoration

[g1]

Much better price as well.
I am not able to check their shipping costs but a place called hawkusa seems to have very good Hammond pricing. But with some others offering free shipping it may not amount to much.

[misterc57]

Order placed with Hawk USA for the 273BX . Thank you all. Will update this thread when the new PT is installed.

[35L6]

How much was shipping ?

[misterc57]

How much was shipping ?

$10. Great prices and reasonable shipping.

[Helmholtz]

Order placed with Hawk USA for the 273BX . Thank you all. Will update this thread when the new PT is installed.

Really curious what output power will be.

[misterc57]

New PT is bolted in, perfect fit with no mods needed. It appears slightly larger than the original.

Question on 6.3 VAC heaters. Filaments are wired in parallel. From PT secondary one end to first 6L6 tube filament, the other end to ground. Center tap has no connection?

Thank you

[Helmholtz]

Question on 6.3 VAC heaters. Filaments are wired in series. From PT secondary one end to first 6L6 tube filament, the other end to ground. Center tap has no connection?

6.3V heater supply means parallel filaments.
You can either ground one end of the winding or the CT, whichever gives lower hum.
Never ground both as this means shorting one half of the winding.

[g1]

Further to what Helmholtz said above, it looks like one side of the filament is grounded in the schematic. (https://music-electronics-forum.com/...6&d=1712437500)
To use the heater center tap you would have to lift all socket heater ground connections and connect to the other side of the heater winding, then connect only the heater center tap to ground.

[Helmholtz]

To use the heater center tap you would have to lift all socket heater ground connections and connect to the other side of the heater winding, then connect only the heater center tap to ground.

So you think they used the chassis as heater ground return?
Passing heater current through the chassis (just to save a bit of wire) would be very bad practice..

[misterc57]

Each preamp tubes pins 4 and 5 are tied together and hard wired to chassis ground. Both power tubes pin 7 are hard wired to chassis ground thread through pin 8.

Power tubes pin 2 and preamp tubes pin 9 are wired together, where one end of the 6.3 VAC heater wire is connected to the first power tube... and the last preamp tube is the end of the line.

The other end of the 6.3 VAC heater will be connected to ground.

Should it matter if the 6.3 VAC wires coming out of the PT are apart or should they be twisted together? There is no reason to believe the original wire was twisted together.

Thank you

[misterc57]

Bias supply that is present is different from the schematics. Most noticeable is the filter cap of 500 uF / 25 VDC (which actually is reading 852 uF. Schematic calls for a 50uF / 50VDC

A couple of different resistor values and an additional 0.033 cap. Also the 220K looks to be a 1/2 watt as it is the same size as the other two resistors.

Thoughts? Thank you

[mozz]

Too big of a first bias cap takes a long time for the bias to get up to voltage. 50uf sounds about right. Does it look original?

[misterc57]

Too big of a first bias cap takes a long time for the bias to get up to voltage. 50uf sounds about right. Does it look original?

Hard to tell if original but after looking at images of other amps I am def. changing to 50uF.

Odd thing also is that the two different schematics I have for this amp have this section configured differently.

[Helmholtz]

Yes, the 500µ cap significantly delays bias ramp-up (maybe up to one minute).
During this time power tubes will be stressed by overcurrent.

[mozz]

I would go with the voltage divider version, I don't like using caps to tap off the HV, seems like it's tough on the caps. You could make it adjustable considering the power transformer is not exact as the original.