Traynor YBA-1 popping circuit breaker

[Beyer160]

I recently picked up a Traynor YBA-4 (a YBA-1 head in 1 1x15" combo), and it sounds absolutely glorious as a guitar amp once I replaced the stock speaker with an Eminence Big Ben. There's just one problem, the amp's circuit breaker pops after about 10 minutes of loud playing. The first time this happened I didn't think to reset the breaker until the next morning (I'd forgotten it had a breaker, I thought I was going to need to get fuses). It came back on, but popped again after a few more minutes of loud playing. Resetting the breaker brought it back to life again, but now I'm in repair mode.

-A previous owner had installed a 3-prong cord, replaced the filter and bias caps and installed an adjustable bias pot, but everything else looks stock. Filter caps look OK (47uf/500v, stock was 40uf/450v), bias is a 47k resistor/20k pot- stock was 39k, so I'm going to replace the 47k resistor with a 22k to try and get the bias a little hotter.

-I calculated 25% and 45% dissipation on the pair of EH 6CA7 power tubes (13 and 23 ma, 471v on the plates), they don't seem to be redplating (I'm amazed how good it sounds with such a cold bias).

-I tested the rectifier diodes (out of circuit) and they were all OK. Replaced them anyway.

-My light bulb current limiter stays off at idle, but lights up when I hit it with signal.



Any thoughts on next steps? I was all set to replace the tubes, but they shouldn't be popping breakers with such a cold bias, right? I figure I'll clean and re-tension the tube sockets because why not, but I'm stumped as to what could be doing this.

It couldn't just be an old, tired breaker could it?

This is the same schematic my amp has in it:
http://www.thetubestore.com/lib/thet...-Schematic.pdf

Thanks in advance for any and all help!

[g1]

It couldn't just be an old, tired breaker could it?

Could be, I recall replacing several in this era of Traynor. Can you monitor the current with an AC ammeter? Or disconnect the breaker and rig it (breaker) to a test jig to see what kind of current is tripping it. Power resistor and variac would do the trick.

[mozz]

These work great for measuring current voltage and wattage. About $20
https://www.amazon.com/P3-P4400-Elec.../dp/B00009MDBU

[Beyer160]

Could be, I recall replacing several in this era of Traynor. Can you monitor the current with an AC ammeter? Or disconnect the breaker and rig it (breaker) to a test jig to see what kind of current is tripping it. Power resistor and variac would do the trick.

My meter has a min/max mode, but I don't have a variac so that's off the table.

Although I hate the idea of punishing my amp more than I already have, would it be dumb to disconnect the breaker and wire an inline fuse holder in its place with the appropriately rated fuse? If that pops, I know the breaker isn't the problem. I have one of these in my parts bucket.

These work great for measuring current voltage and wattage. About $20
https://www.amazon.com/P3-P4400-Elec.../dp/B00009MDBU

[ATTACH=CONFIG]44344[/ATTACH]

That's pretty cool!


Oh, and I goofed in my calculations- the 47K bias resistor is perfectly fine, I goosed it up to 48%/65% dissiaption (36/26 mA).

[cjenrick]

yeah the spring gets tired, had a drunken tv Shop boss that used to take us kids out on service calls, use to wrap wire around the circuit breaker contacts so the set would run, holy crap, i mean can you say house fire? lord mercy still gives me chills.

[Enzo]

Breakers do wear out, it could be as simple as that.

Bias might be fine, but tubes can still fail. An intermittent short in a tube can pop a breaker but the tube still biases up OK.

A note on testing. YOu pulled diodes and tested them, but I suspect your test was with your meter. Your meter puts a volt or two on the parts and tiny currents. But the meter never puts 400v on a diode nor runs substantial current through it. Your meter then can identify shorted or open or super leaky parts - in other words bad ones. But what it cannot do is assure you a part is good. So if in doubt, just replace them, which you already did.

I agree you need to test it for current draw from the mains. If it has a 3A breaker, and you see 2.8A running through it at idle, it takes very little to push it over the top. But if the amp is only drawing 1A at idle, then clearly some event is tripping the breaker, or the breaker itself is defective.

[The Dude]

......Bias might be fine, but tubes can still fail. An intermittent short in a tube can pop a breaker but the tube still biases up OK......

^^^^^^That. Try a new or known good set of output tubes.

[g1]

Yes, the in-line fuse holder is a good test, make sure you use a slow-blow fuse.
You said you were amazed at how good it sounded with cold bias, why on earth would you want to increase it and decrease your tube life?
Does it sound even better? If not, please ignore any 'magic numbers' you may have read about.

[Beyer160]

Breakers do wear out, it could be as simple as that.

We get power strips at work sometimes that have tripped too many times and get "soft". This amp is probably 45 years old, a bad breaker wouldn't surprise me. It's so easy to access the inside of these things (the top comes off with four screws- thanks Pete Traynor!) I'll just put the inline holder in.

Bias might be fine, but tubes can still fail. An intermittent short in a tube can pop a breaker but the tube still biases up OK.

A note on testing. YOu pulled diodes and tested them, but I suspect your test was with your meter. Your meter puts a volt or two on the parts and tiny currents. But the meter never puts 400v on a diode nor runs substantial current through it. Your meter then can identify shorted or open or super leaky parts - in other words bad ones. But what it cannot do is assure you a part is good. So if in doubt, just replace them, which you already did.

Looks like I'm in for some new tubes, then.

I learned the hard way about diodes- I essentially rebuilt my '67 Gemini, but left the diode rectifier untouched. Not long after reassembling the amp, one of those damn diodes died.

I agree you need to test it for current draw from the mains. If it has a 3A breaker, and you see 2.8A running through it at idle, it takes very little to push it over the top. But if the amp is only drawing 1A at idle, then clearly some event is tripping the breaker, or the breaker itself is defective.

Would this be as simple as just measuring amperage across the breaker?

You said you were amazed at how good it sounded with cold bias, why on earth would you want to increase it and decrease your tube life?
Does it sound even better? If not, please ignore any 'magic numbers' you may have read about.

Because maybe I can make it sound MORE amazing!

I figured it was worth trying, my Gemini really came alive with a hotter bias. You're right though- if I don't hear an improvement, I'll change it back. No need to cook the tubes if I don't have to.

[g1]

You would have to measure the amperage in series with the breaker (not across). The max mode would probably work well.
If I recall, the number on that breaker is a 'hold' rating and it opens at some point above that rating.

[Enzo]

Not across the breaker, current is a series thing. Think about it, a non-tripped breaker is a short circuit, so there is zero volts end to end. Until it trips. A current meter in parallel the low resistance breaker won't show anything useful, if anything at all.

So it is as simple as putting a current meter in series with the breaker or usually the amp itself. I have a metered outlet I use for the unit under test on my bench.

Traynor amps always got my vote for working in, and especially for someone wanting a chassis for their own circuits. They are built very solidly, and have great access, and inside there is enough room for you to climb in there with a case of beer and hang out while you work, maybe even room to bring a friend. No problem adding a few extra tube sockets for example.

[Beyer160]

So here's where I'm at now:

-After replacing the breaker with a fuse, the fuse popped after a few minutes of play. Wired the breaker back in.

-Bought a new set of EH 6CA7s. These were more evenly matched than the old ones, biased up fine, fairly cold (30% ish). Popped the breaker even faster this time, with a distinct burning smell. I don't see any obviously damaged components. Resetting the breaker allowed the amp to power up again, but I shut it down again immediately. I've abused the poor thing enough.

Later, I discovered a messageboard post warning that EH 6CA7s weren't pentodes like original 6CA7s, but instead beam tetrodes. Apparently this is OK in certain amps like Marshall and Music Man, but not Traynors because pins 1 and 8 are tied to ground. This is where my shaky technical knowledge drops off- what does this mean? Could this be the source of my amp's unhappiness? If not, anyone have suggestions on next steps?

[Enzo]

No, pins 1 and 8 should be connected together (usually to ground) regardless.

Power it up with no power tubes. You can leave in the small tubes if you like. Does it still pop fuses? Also, does it pop a fuse even if in standby, or only if the standby switch is in operate mode?

get out an AC ammeter and measure current draw while it idles. How much current is it using?

A visual inspection is always important, but the vast majority of bad parts look exactly like good parts. And your problem may not be a bad part, but could be a short between two adjacent things.

[g1]

The problem is for Traynors like the YBA-3 that tie the suppressor grid (pin1) to the negative bias for the grids.
If you use the EH6CA7's in those type amps, it grounds out the negative bias and leads to disaster.
Your YBA-4 should not be wired like that, unless someone modified it.

[Enzo]

Aha, I didn't think of that.