The Amp Garage

Is it plausible that an h-k short caused the failure of this PT?

So the last measurements of the existing PT had 460v across the Secondary and 6.3vac for the heaters.... that's all there is.

All the heaters are off of the same winding at 6.3v so Steve, it makes sense to continue in that fashion.

Yes that will work electronic wise, ( don’t know about physical wise ) but you will need to add another dropping resistor before the first filter node to bring down the 360 volts that you will have off of the 275-275 windings down to the stock schematic reading of 235. I would say that if you get t...

Thanks Martin, Max and Steve, waiting for owner to give me go ahead. No need for Int. so 290 HAX seems best. Will still need a dropping R and look at bias.

A

https://www.hammfg.com/files/parts/pdf/290HAEX.pdf

This has 275/0/275 136ma. and the mounting holes are spot on. has the 6.3vac

The Primary is a bit strange but I can see a good option with 120vac

Ya think this will fly?

Hey guys, yeah so looking at Hammond, I need to source a horizontal mount not vertical. Appreciate eyes and analysis on this. I'll get back when I get the PT and see how it goes.

P-TGP-001. over at AE?

Best A

I do not see a CT on the heater winding, on the schematic or within the amp. Rather the heaters are grounded by way of the light bulb frame.

A

Yup, it's also vibrating strangely, not a hum. Now to figure out what caused it. I tried to measure the Heater voltage and that lit up the limiter??

Any thoughts on replacement PT?? Hammond?

A

Ok with Red1 being the Left of pic and Red2 right

R1 -YR - 720K ohms
R2 - YR - 145 ohms
R1 - R2 - 720k ohms
YR - W - 165 ohms
R1 - W - 720k ohms
R2- W - 300 ohms

Not what you would expect

The white wire (which was grounded originally) shows continuity to the red yellow wire (was also grounded). I see a version of this amp on offset guitars and those wires are correct when grounded, but they are causing a short when they both are in circuit. I do not get continuity on that white wire ...

With the red and yellow wire added no short

With the white wire added no short

with both of those wires added yes I get a short. ??

Ok, so they had these grounds bunched up together. The Mains ground, the cap ground and then the secondary ground and the heater grounds. I leave the mains and cap grounds on but pull the other two. The schematic shows a Transformer chassis ground I think, I don't see that. Ok so with just the secon...

Good info thanks Johnny

Heaters show 35 ohms, primaries are at 7 ohms , Plates are at 350 ohms.

Thanks Max. Amp plays very well at the moment. I am going to let the owner decide about re-coning. I have provide several reputable places that have experience re-coning Field Coil type speakers.