Tray or YBA-1A Very Low Output - Please Help

[Helmholtz]

And they were no harder on tubes than other high power amps.

Not convinced.
Some designs stand the test of time - others don't.
Also B+ might have been closer to 500V and thus power more like 70W in the early days.
A 10% increase of mains voltage roughly increases power output by 20%.

All I said above refers to EL34s.
6550s or KT88s would be fine with the conditions in the amp.

[mozz]

Helmholtz is quoting from the Telefunken EL34 datasheet, 11K and high voltage, 90w. At 4K it shows 70w. I think the factory tubes were GE?, dimples on top,but are most likely Euro made. Mine came with a 8x10 cabinet with a mis-mash up of speakers so i can't say what the impedance was. Last time i played it thru a 4x12 with vintage 30's, you could feel every pick movement thru your chest, few songs from master of reality, neighbors did call up the wife and complain.

[g1]

I can only tell you from my (Toronto) experience. You do not have to believe it.
Also, if they were extra hard on tubes, I think that would be the first thing people would say about them. But they don't say that. What you mostly hear is "you can't get 90watts out of a pair of EL34s".
There are still tons (literally ) of these out in the field, working with EL34's. There is no major push about converting to 6550 etc.
I don't want to sound argumentative, this controversy has played out many times, but usually about the power output.
I really would like to know why they got away with it.

[Helmholtz]

. What you mostly hear is "you can't get 90watts out of a pair of EL34s".
.

As stated above, you can (don't try that with 6L6s). I have an old Siemens amp that proves it.
But with an Raa of 3.8k this means plate overdissipation at medium output. At full output plate dissipation is lower than at medium output.
Some tubes may take it - others will not survive very long.
I don't like to change my power tubes once a year.

[Chuck H]

I can only tell you from my (Toronto) experience. You do not have to believe it.
Also, if they were extra hard on tubes, I think that would be the first thing people would say about them. But they don't say that. What you mostly hear is "you can't get 90watts out of a pair of EL34s".
There are still tons (literally ) of these out in the field, working with EL34's. There is no major push about converting to 6550 etc.
I don't want to sound argumentative, this controversy has played out many times, but usually about the power output.
I really would like to know why they got away with it.

I've been on the antagonist side of that argument regarding Traynor amps right here on the forum. I won't trouble to look it up, but... I was wrong. The amp is question absolutely was making the power reported. Scope shots were provided because it was important to the poster (can't remember who now) to SHOW me that I was wrong. IIRC the amp in question was an EL84 amp running a pair and producing 24 watts of sine wave. I said it was impossible and the scope shots proved otherwise. I guess this wouldn't be considered "RMS" power because the scope doesn't show that. But there it was. 24 watts into the load just barely compressing on the sine wave. Sorry I can't remember more details but I'd be gun shy to poo poo any Traynor amp output claim after that.

[loudthud]

I had a new YBA-1A in early 1970. It had the 400-0-400 PT and the enormous OT. Bias was not adjustable, I had to install a pot when I replaced the tubes. It had EL34s and you could see the screens glowing a dull red. There are early schematics that call for 7027As, not sure if they were YBA-1 or YBA-1A, but I've never seen one of those amps in the USA.

One thing not mentioned, and you won't find it on any data sheet. They ran the suppressor grid (pin 1) of the EL34s at -60V. Some people say that's how the EL34s survived.

[mozz]

There's also the fan, whether that will actually allow you to run tubes higher than their rating would seem to make sense.

[Helmholtz]

Yes, according to Tomer cooling the bulb can increase tube life.

[g1]

There are early schematics that call for 7027As, not sure if they were YBA-1 or YBA-1A, but I've never seen one of those amps in the USA.

They were the YBA1. I have one here right now. It has a plate over the hole where the earlier ones had tube rectifier. And has the choke. This one is from 1971.
Has GE 7027's and a couple of the preamp tubes are Rogers branded. It's fairly common to find the Rogers preamp tubes in them which is what they came out of the factory with as far as I know.
Even in this 'lower powered' variant, the PT is huge. ( the biggest PT in Chuck's post #40)

[Helmholtz]

To be clear, I'm not surprized by high output as this is a logical consequence of high B+ and little sag at full power.
What makes me wonder, though, is that the excessive PD doesn't cause early tube failures with EL34s.