Hi all,
Just finished a ST-35 build. I am using an Edcor xpwr005-120 power transformer. My voltages are a little high. B+is 388. Heaters are a little low 2.7 on pins 4 and 5. Any cause for concern? Should I lower it? If so how? Tia
Al
High voltage
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High voltage
by apurcell22 » Mon Nov 08, 2010 10:53 am
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by Ty_Bower » Mon Nov 08, 2010 11:30 am
My ST35 was built from an old Allied power transformer, and the B+ is usually just a little over 400VDC. I adjusted the bias to keep the idle current closer to 32mA and it seems to be OK with that.
The heater readings are a bit curious. Some meters don't give very accurate measurements of AC voltages. Do you have another meter you could use to double check?
The heater readings are a bit curious. Some meters don't give very accurate measurements of AC voltages. Do you have another meter you could use to double check?
"It's a different experience; the noise occlusion, crisp, clear sound, and defined powerful bass. Strong bass does not corrupt the higher frequencies, giving a very different overall feel of the sound, one that is, in my opinion, quite unique."
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by TomMcNally » Mon Nov 08, 2010 11:33 am
Is the B+ measurement with the tubes in?
Are you measuring the filament voltage with the meter set to AC
and across the pins?
Do you have R-36 and R-37 in the circuit? They can be jumped out.
Are you measuring the filament voltage with the meter set to AC
and across the pins?
Do you have R-36 and R-37 in the circuit? They can be jumped out.
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by TomMcNally » Mon Nov 08, 2010 11:59 am
The choke would be in place of R-34 and R-35, R-36 and R-37 are in series with the filament power, and can be jumped out to increase the voltage.
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by TomMcNally » Mon Nov 08, 2010 12:12 pm
With the resistors jumped out, you should get 5.9 at the tubes.
That's close enough.
That's close enough.
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by TomMcNally » Mon Nov 08, 2010 12:17 pm
Ty says his runs 400 ... I wouldn't worry about it.
Personally, I don't measure voltages (except when setting bias)
if it works, it's good. Tubes have a wide tolerance.
... tom
Personally, I don't measure voltages (except when setting bias)
if it works, it's good. Tubes have a wide tolerance.
... tom
Last edited by TomMcNally on Mon Nov 08, 2010 12:32 pm, edited 1 time in total.
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by Ty_Bower » Mon Nov 08, 2010 2:06 pm
TomMcNally wrote:Ty says his runs 400 ... I wouldn't worry about it.
Yep. It's been that way for quite some time now. I adjusted the bias to get an idle current closer to 32mA, but I'm not even sure that was necessary.
"It's a different experience; the noise occlusion, crisp, clear sound, and defined powerful bass. Strong bass does not corrupt the higher frequencies, giving a very different overall feel of the sound, one that is, in my opinion, quite unique."
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by apurcell22 » Mon Nov 08, 2010 2:09 pm
Fixed the heaters. This little amp rocks! B+ doesn't seem to be an issue. Ran the amp for about 40 minutes no red plates. I will upload pics soon.
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