Seduction + C4S eating tubes. Compatibility?

[tiller]

OK. So, cracked open the Seduction this morning. Didn't see any suspicious looking capacitors, but I did decide to reflow some solder joints. I reflowed joints around the diodes in the rectifier, as well as the 1.2ohm resistor, 10000uF filter cap, and one of two tube socket pin 4s that looked a bit sketchy. I checked heater voltages after reflowing the PSU joints and now my heaters are both reading 5.1V with tubes installed. Reflowing the Pin 4 made no difference. Definitely an improvement there as now both tubes are the same and a little closer to spec.

Checked the resistance of the 1.2ohm resistor and its pretty much spot on when I take meter resistance into account. I also shorted out the 1.2ohm resistor and tested the voltage to ground. I get 9.6V without tubes installed.

Last but not least I had a look through my spares and I have a couple 5W 3ohm Dale resistors I could parallel with the 1.2ohm.

So far so good!

[Paul Birkeland]

What is your AC wall voltage?

[tiller]

DMM is telling me 117.3V +- .1V

[tiller]

Paul - any tips as to where to proceed from here?

[Paul Joppa]

Try paralleling both 3-ohm resistors AND the current 1.2 ohm resistor. My old notes say this should be very close to the right voltage, but please do report the filament voltage you get so I can check.

Incidentally, I am assuming you have the PT-1 power transformer, with the silvery tape around the core. Let us know if it's the older version with a split-bobbin transformer.

[tiller]

Okay, paralleled both 3ohm resistors with the 1.2ohm (so effectively .69ohm) and fired it up. I'm now reading 5.4Vdc at Pin 5 referenced to ground, with old EH tubes in place, and 5.7Vdc with a pair of fresh NOS Tesla. I thought for sure it would have gone up more than that.

Transformer is the PT-1 with silver tape around the core, yes.

Thoughts?

P.S. I get the same values when taking the measurement on the hot side of the 10000uf cap as well.

[Paul Joppa]

OK - thanks for the numbers; I estimate that you want a 0.27 ohm resistance of at least 1 watt rating. Probably anything 0.22 to 0.39 will be close enough. That should get you 5.7-6.0 volts depending on the tube, and that's my design range for this particular preamp.

[tiller]

Thanks for the help Paul. It seems in spec with the new tubes then
 I will run it this way until I place an order for some parts in the future and pick up a more appropriate resistor.

 Thanks again!

Adam