HV Arc

For those building and repairing amps on their own. Learna and share ideas.

HV Arc

Postby Kid on Wed Aug 25, 2010 6:42 pm

Hello again,
Got my new set of tubes today, fired my B-15N Clone up (/w my computer headphone output, a friend still has my p-bass knockoff) sounds great - clean, lots of tone control :). Had an HV arc occur twice in V4 though (last power tube, as is single channel), I see the kill-a-watt in the wall is reading about 128 now when I look though - don't know what it was at the time of test (B+ was high then, did not check the wall - was on lunchbreak). Power co. is having major problems and upgrading too. Will try on cleaner power, report later...
With really high B+ would an arc like this occur?
Thanks,
Damien
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Re: HV Arc

Postby PeterS on Wed Aug 25, 2010 8:35 pm

How high is the B+ in the amp, and what brand of power tubes are you using?
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Re: HV Arc

Postby Kid on Wed Aug 25, 2010 11:49 pm

PeterS wrote:How high is the B+ in the amp, and what brand of power tubes are you using?

B+ is high by slightly more than 20% across the board, but am at about 127 VAC at wall outlet. Am using Tung-Sol new production tubes.
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Re: HV Arc

Postby PeterS on Thu Aug 26, 2010 3:04 am

B+ is high by slightly more than 20% across the board


So how many volts is it?
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Re: HV Arc

Postby Kid on Thu Aug 26, 2010 12:45 pm

V1 Spec Actual
Pin 5 165 206
Pin 2 175 236

V2 Spec Actual
Pin 5 225 273
Pin 2 235 310

V3/4 Spec Actual
Pins4 445 547
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Re: HV Arc

Postby PeterS on Thu Aug 26, 2010 4:45 pm

It could be 547 volts is just too much for those tubes. IMO the best solution would be to get some old production 6L6. They don't need to be NOS, just buy enough pulls to find a good pair and they'll last a long time...
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Re: HV Arc

Postby Kid on Fri Aug 27, 2010 6:15 pm

PeterS wrote:It could be 547 volts is just too much for those tubes.

Hate to say it, but my impatience has cost me yet again, the second set of tubes slowly died. Had only a 4 ohm 12" laying around and the hammond OT purchased had 4 ohm taps..... Could it be the lack of proper load causing the B+ to be too high? (I built the thing to exacting specs with respect to resistors & Caps).
PeterS wrote:IMO the best solution would be to get some old production 6L6.

What brand exactly would you recommend?
Thanks again for all your help
Damien
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Re: HV Arc

Postby PeterS on Sat Aug 28, 2010 1:33 am

You'll find B+ goes up and down a bit as you vary the bias current, but not a huge amount. The speaker load shouldn't affect it.

I don't have a brand recommendation, I'm too tin-eared to hear the subtle differences others hear (or imagine). But all the old USA brands are good AFAIK.
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Re: HV Arc

Postby Gooch on Sat Aug 28, 2010 2:24 am

You can still pick up the JAN Phillips 6L6WGC for a pretty good price. I'd try a set of them. Optimal would be some old 7581A or 7027A tubes, but you're gonna pay for them. :cry:
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Re: B-15-N Build Help

Postby Kid on Fri Jul 05, 2013 11:19 pm

PeterS wrote:IMO the best solution would be to get some old production 6L6.


Got a complement of mid-60's RCA, think the rectifier may be a Philips Mullard Re-Brand.

To be honest (at the time guess I knew no better) when I first sourced this I got a 25 Watt Hammond OPT with no regard to primary resistance, which was 38% too high. Am thinking this was the cause of that HV arc between the OPT and Power Tube.

Then relied on info from a thread elsewhere (the guy seemed knowledgeable), and replaced OPT with another that was still 20% too high on the primary. Think perhaps he messed up the 208 and 214 specs. Would this have been a major contributing factor to the B+ being 20% too high?

Am still confident all the resistors and caps are spot on (actually tore through at some point and checked all the resistors). Have the appropriate 5,500 Ohm/30W on hand to install this weekend. Think it would be a great sin to ruin any of this vintage glass. To be sure, I can install the rectifier alone first and check my B+ right?

The supplier of the power tubes also recommended running at half volume for 20 hours and then checking the bias, make sense?

Any and all input would be greatly appreciated.

THX again guys,
Damien
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