TSL122 100 to 50 watt

[ivanppg]

Hi, I just got a TSL122 combo, two tubes are glowing normally, one is complettely dead and the other is glowing maybe a little and has some blue light. I've got and idea to take off those two bad ones and run It with only 2 tubes on the "50 watt mode" ;p

Is this possible with not much tech stuff?
My speakers are wired for 16 ohms so should I plug it into 8ohm output?
Can you tell me how to do that safely?
Thanks!
Greetings from Poland!

 

[Jethro Rocker]

Why? Just get 2 new tubes, ot better yet, 4. Easy to bias points right on the back. Could be issues with sockets or runaway bias too.
I wouldn't bother, honestly.

 

[ivanppg]

Why? Just get 2 new tubes, ot better yet, 4. Easy to bias points right on the back. Could be issues with sockets or runaway bias too.
I wouldn't bother, honestly.

Im so poor man
I can do that but that was my first idea. If it will be possible then very very good.

 

[Jethro Rocker]

I should add - did the amp work when you got it? Have you tested it at all?
It should work 2 outer and 2 inner tubes together. So which ones are bad?
It's really not the best idea not knowing if the tubes are an issue or something else

 

[ivanppg]

I should add - did the amp wo4k when you got it? Have you tested it at all?
It should work 2 outer and 2 inner tubes together.

Yeah, It lives, i just got it hour ago plugged it in and saw that tubes, It plays, sounds good, maybe little flat and cold but TSLs are like this i guess. It has some rattling sound at the back, not sure if it's a reverb tank or the tube, is it possible that loose tube can rattle when played? Its 122 combo

Edit: 2 inner are bad, outer seem to be good.

 

[Jethro Rocker]

If one tube doesn't even light up and it plays and sounds good, something is funny. Does that tube light up when playing at all?
TSL122 is not flat and cold at all.
Could be reverb tank or tube retainers?
If one tube doesn't light I would strongly recommend not to play it anymore.
Sadly when you have a tube amp you should have spare tubes even if you are broke.

 

[ivanppg]

If one tube doesn't even light up and it plays and sounds good, something is funny. Does that tube light up when playing at all?
TSL122 is not flat and cold at all.
Could be reverb tank or tube retainers?
If one tube doesn't light I would strongly recommend not to play it anymore.
Sadly when you have a tube amp you should have spare tubes even if you are broke.

Will check It tommorow...

 

[Tatzmann]

For now you can try to re-seat the not working ones, it might be bad contact on the pins due to oxide buildup.

Not unusual if an amp was stored in a cellar,
shed or attic. I had such cases.

Pull the powerplug.

Pull the valves carefully out at the "base" not at the glass and put em back in.

Power up the amp and check for filament glow.

 

[Pete Farrington]

the other is glowing maybe a little and has some blue light.

Nothing there indicates a problem.
Provided the valve gets hot, the degree of visible glow is immaterial.

 

[Jethro Rocker]

Nothing there indicates a problem.
Provided the valve gets hot, the degree of visible glow is immaterial.

But normally even the heaters provide some glow on an EL34. Yes if it heats I guess that much works. OP should check heat from that tube.

 

[Pete Farrington]

Yes, it’s incorrect to equate ’not much glow’ to ‘valve not reaching operating temperature’.
People read so much into it, but in reality the degree of visible glow is totally random, an uncontrolled characteristic.

 

[Jethro Rocker]

Yes, it’s incorrect to equate ’not much glow’ to ‘valve not reaching operating temperature’.
People read so much into it, but in reality the degree of visible glow is totally random, an uncontrolled characteristic.

OP and picture indicates zero light, which would be an issue. Heaters do show some glow for sure.

 

[ivanppg]

Okay, update, I pulled out all tubes, relocated the inner ones, outer put in the place as it was.
Now the 3 tubes glow normally, one don't glow and it's the one that had been dead previously. Checked bias, one pin around 43mV, other one +/- 38mV.
Do I need to replace one bad/two inner or all 4 tubes?

 

[Tatzmann]

If you cant afford new tubes at the moment then just play it with only 2 working powertubes installed, one at each side.

Either like this

O-x-x-O or this x-O-O-x

Set the bias between 30 and 35mA(measured in mV) at each side.

Its universally agreed upon that you use half the output impedance, if you have a 16ohm speakerload you would use the 8ohm output jack on the amp.

One tube seems bad, might got gassy.
The remaining one you keep as a spare.

 

[Pete Farrington]

Either like this

O-x-x-O or this x-O-O-x

Or
O-x-O-x
or
x-O-x-O

The ‘inner / outer pairs’ terminology is a convenient way to put the idea across of balancing the push pull sides, but isn’t an electrically valid concept.
Hence I feel a little uneasy about it being promulgated

It’s worth noting that halving the number of output valves halves the load on the HT supply, making it twice as stiff.
Hence if the amp gets cranked up to high power outputs, the remaining valves will be under more stress, because the intended degree of sag won’t be happening.
The point being that it’s should be viewed as a short term measure, not as a long term way forward, and not as a means of intentionally halving the amp’s power output. eg if cranking it into an attenuator or at a ‘loud but not 100W loud’ gig.

 

[Jethro Rocker]

At minimum replace a pair. You don't know when or why the one failed which puts a strain on it's partner/

The ‘inner / outer pairs’ terminology is a convenient way to put the idea across of balancing the push pull sides, but isn’t an electrically valid concept.

Is that not how the amp runs the push pull? Outer together and inner together? Therefore does it not make sense to leave either pair in amp instead of willy nilly?
Either way though, a very short term solution as again, not sure why the one tube dies, perhaps just it's time.
When all tubes working Marshall recommends 45mV per tube (90 per side) which may seem way high. Some people go really low, I like some sizzle and mine is set around 84 per side .
With all 4 tubes.

 

[Dr.Twang!]

Is that not how the amp runs the push pull? Outer together and inner together? Therefore does it not make sense to leave either pair in amp instead of willy nilly?

The output tube sockets are wired in parallel in a push pull class AB amp. (LH sockets/RH sockets-1/1 on a 50w, 2/2 on 100, 3/3 on SVT for instance)
For this discussion, pin 3 on the two left sockets are wired together as are pins 3 on the right sockets.
Even running with 2 tubes pulled (one on either side of the push-pull pair) the bias requirements and max dissipation remain the same for each tube regardless. So with current draw method on the TSL bias probe pins you would want to read 1/2 the recommended current draw of 4 output tubes(2 on a side)
Because they are in parallel, the plate to plate impedance would be double with only 2 tubes on the output transformer secondary winding, hence the speaker load impedance matching adjustment.
As Pete pointed out (and I learned years ago with Superleads) pulling 2 output tubes actually unloads the power supply, making it stiffer and never gave me the results I was looking for: earlier breakup and low volume.

 

[Dogs of Doom]

the thing is, from what I understand, the tubes are paired by 2 inner & 2 outer

let's just say that the inner x00x are push & outer 0xx0 are pull, in the push/pull setup.

as Pete said, you'd want 1 inner & 1 outer to get the push/pull. If you simply pull 2 inners, or 2 outers, then you'll only get push, or pull... In that, most people think that having space between the 2, is better than having the 2 next to each other, which is why he suggests the staggered tubes. x0x0 or 0x0x

 

[Dr.Twang!]

as Pete said, you'd want 1 inner & 1 outer to get the push/pull.

Actually, you need 1 LH & 1 RH. Either socket on that side will work- one or two tubes on only one side sounds horrible. Try it.

 

[Jethro Rocker]

Ok. That explains it for me .thanks.
That said, short term only. OP shoild get 2 more tubes minimum