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6BM8 power supply

Quick question. On the 6BM8 power supply, the B+ is specified as 225v. I have my Hammond 269EX wired to my 120v mains using the white, or 115v tap. I am getting 238v for B+ and 3.5v*2 for heater voltage. I would guess that I need to rewire my input ac to the 125 tap on the transformer to bring these back in line.

Or is this 'clode enough"?

Roger

6 answers0 replies

6 Comments

Roger Ayotte

Jun 19, 2023

I get that the tubes are not identical. on further inspection I found that the voltage on pin 9 is vastly different.

217vdc on one and 125vdc on the other, and the diffference moves with the tubes. I suspect that I have a bad tube.

I DID drop these tubes onto the floor, so although they might have been bad to begin with, I suspect I damaged one of them.

Thanks for all the help, I will be replacing these tubes.

Roger

Skunkie

Jun 20, 2023

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Replying to

Yeah that is WAY different and if it follows the tube, you know your wiring is good.

Skunkie

Jun 16, 2023

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I use the 125V taps, but also: is this with the tubes installed and everything loaded?

Roger Ayotte

Jun 18, 2023

Replying to

The tubes were installed, dummies on the output, no input. I switched to using the 125v taps and now I am getting 220v on my B+.

Now for something else. After switching the tap to 125v, checking voltages around the amp, I note that where you have indicated 220vjust after the 4.7k ohm and above the 33uf cap, the voltage on one side is 218v and the other channel is 213v.

I checked the resistance of the 4.7k ohm resistors and they are both 4.7k. Either I have more curent going through that channel, or the cap is leaking?

I DID have an issue with wiring up the 125v tap and accidentally hooked up the black and greay wires (I know, I know!) for a brief time at about 30vac. Nothing I saw was effected, but I worry.

What reasons could there be for the discrepancy between the channels?

Roger

Danny

Jun 19, 2023

Replying to

The tubes will conduct a little different between the sides and the closer matched the tubes are will be closer - 213v and 218v on the other channel is nothing to be concerned about - your good!

Skunkie

Jun 19, 2023

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Replying to

Because tubes aren't identical. That's nothing to be concerned with.