new build 36lite with vvr

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Re: new build 36lite with vvr

Post by Bieworm »

In which sockets are the EL84 pair put?
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Re: new build 36lite with vvr

Post by chaliapin »

Tubes in sockets 3 and 5 currently.

Thanks Josh, I'll do as you suggest.
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Re: new build 36lite with vvr

Post by chaliapin »

Is checking solder joints just a visual check or should I do a continuity check or something?
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Re: new build 36lite with vvr

Post by Bieworm »

chaliapin wrote:
Mon 01/16/23 2:47 am
Tubes in sockets 3 and 5 currently.

Thanks Josh, I'll do as you suggest.
3+5????
Then each tube has a separate 150R cathode resistor. That's bad!
They should share one 150R (or preferably 180R) per pair. You should put tubes in V3+V6 or V4+V5... try that! I hope you didn't ruin those 2 good tubes too... they have been pulling twice the current they are supposed to pull.. hence your redplating and excessive hummmmmmmmm
36W chaliapin.png
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Re: new build 36lite with vvr

Post by JMPGuitars »

Bieworm wrote:
Mon 01/16/23 6:25 am
chaliapin wrote:
Mon 01/16/23 2:47 am
Tubes in sockets 3 and 5 currently.

Thanks Josh, I'll do as you suggest.
3+5????
Then each tube has a separate 150R cathode resistor. That's bad!
They should share one 150R (or preferably 180R) per pair. You should put tubes in V3+V6 or V4+V5... try that! I hope you didn't ruin those 2 good tubes too... they have been pulling twice the current they are supposed to pull.. hence your redplating and excessive hummmmmmmmm
36W chaliapin.png
Actually, you're half right. He can't have just 2 tubes in without changing the cathode resistors, that is why he's redplating. I was mistaken when I looked at it previously, just opposite of how you were mistaken lol.

But he can't put them in as you suggest either. You have to consider the OT as well (refer to the schematic).

What he should do is rewire 3+5 to share a single 180 ohm resistor until he gets more tubes (or more resistors) and he can wire according to the schematic.

To make the amp switchable between 2 or 4 tubes, he'd need to user higher value cathode resistors, and use 4 (1 per tube).
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Re: new build 36lite with vvr

Post by chaliapin »

Balls, ok, they're now in 3 and six, I thought I wanted one in each side.

Straight after standby going on all looks ok
B plus 318

Power tubes
Pin 3 11.4v
Pin 7 350v
Pin 9 333v

But then after maybe ten seconds in starts getting warm, b plus going up to 350, pin 7 coming down, pin 3 going up, then i panic and switch off. Will sit down and do more with the highlighter later.

Amp voltages appear to be stable with the bulb limiter.
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Re: new build 36lite with vvr

Post by JMPGuitars »

chaliapin wrote:
Mon 01/16/23 9:27 am
Balls, ok, they're now in 3 and six, I thought I wanted one in each side.

Straight after standby going on all looks ok
B plus 318

Power tubes
Pin 3 11.4v
Pin 7 350v
Pin 9 333v

But then after maybe ten seconds in starts getting warm, b plus going up to 350, pin 7 coming down, pin 3 going up, then i panic and switch off. Will sit down and do more with the highlighter later.

Amp voltages appear to be stable with the bulb limiter.
See my previous reply. Neither way will work with what you're trying to do.
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Re: new build 36lite with vvr

Post by chaliapin »

Can I add a lower wattage value resistor in series with the big 150r ones?

Sorry I wrote my previous post before I read your last
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Re: new build 36lite with vvr

Post by Bieworm »

JMPGuitars wrote:
Mon 01/16/23 9:52 am
chaliapin wrote:
Mon 01/16/23 9:27 am
Balls, ok, they're now in 3 and six, I thought I wanted one in each side.

Straight after standby going on all looks ok
B plus 318

Power tubes
Pin 3 11.4v
Pin 7 350v
Pin 9 333v

But then after maybe ten seconds in starts getting warm, b plus going up to 350, pin 7 coming down, pin 3 going up, then i panic and switch off. Will sit down and do more with the highlighter later.

Amp voltages appear to be stable with the bulb limiter.
See my previous reply. Neither way will work with what you're trying to do.
When on 2 tubes , shouldn’t he also switch the speaker impedance switch to virtually match the load?
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Re: new build 36lite with vvr

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chaliapin wrote:
Mon 01/16/23 10:07 am
Can I add a lower wattage value resistor in series with the big 150r ones?

Sorry I wrote my previous post before I read your last
Define lower…
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Re: new build 36lite with vvr

Post by chaliapin »

Err, yeah, good question, I only have 100r quarter watt. So if I rewire 3 and five to share the single cathode resistor do I basically have an 18watter for now?
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Re: new build 36lite with vvr

Post by Bieworm »

chaliapin wrote:
Mon 01/16/23 11:00 am
Err, yeah, good question, I only have 100r quarter watt. So if I rewire 3 and five to share the single cathode resistor do I basically have an 18watter for now?
Quarter watt? LOL !!! I think those will ignite instantaneously 😎
Just rewire 3 and 5. Daisychain their cathodes (pins 3)to one of those 150R resistors. Then you have an 18 watt. Also set the imprdance switch to 4 ohms on a 8 ohm speaker, or 8 ohms on a 16 ohm speaker to match the OT primary with the secondary.
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Re: new build 36lite with vvr

Post by chaliapin »

Ok, so v3 and v5 are now sharing the cathode connection. They don't share the resistor connecting pin 9 to point b, there's currently one for v3 and 4 one for v5 and 6 do I need to change that so it's the same as the 18w schematic as well?
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Re: new build 36lite with vvr

Post by Bieworm »

chaliapin wrote:
Mon 01/16/23 12:47 pm
Ok, so v3 and v5 are now sharing the cathode connection. They don't share the resistor connecting pin 9 to point b, there's currently one for v3 and 4 one for v5 and 6 do I need to change that so it's the same as the 18w schematic as well?
When you don’t have any other EL84’s installed it should resemble the 18 watt doing it that way. Flip it on first with the bulb, and if ok.. test without bulb
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Re: new build 36lite with vvr

Post by chaliapin »

Well I really thought that was going to sort it out but around 20 seconds after switching on the standby the bulb starts getting brighter. Without the bulb limiter the b plus starts to rise and the humming begins. I'll get back to the painstaking checking but any ideas what I might be looking for would be great.
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Re: new build 36lite with vvr

Post by chaliapin »

Another highlighter test done. No lightbulb moments. Haha. Sob.

Things maybe worth mentioning.

The resistor from a-b is not 1k but 1.5k.

V2 is grounded with the pre amp and inputs, not the power amp.

The screen from the mains side of the PT is grounded through a fuse to the star ground. The ct for 275v supply to the rectifier is also grounded there.

I honestly can't think of anything else im unsure of or haven't checked. I know I know, there must BE something...

Thanks for all your patience, mine is wearing a little thin with myself...
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Re: new build 36lite with vvr

Post by JMPGuitars »

chaliapin wrote:
Mon 01/16/23 2:53 pm
Without the bulb limiter the b plus starts to rise and the humming begins.
What does this mean? You need to be specific so we can help you. The B+ rises? To what? Does it stabilize? Or does it count to infinity (and beyond)?

Ignore the hum for a moment and get useful information.
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Re: new build 36lite with vvr

Post by chaliapin »

Sorry, I get nervous when it starts humming and heating like it's going to blow up in my face...

Weirdly, it's behaving a little different this morning.

With standby off I have 230vac and 310vdc rectified at the standby switch.

Standby on

B+ 354
P3 11.6
P7 350
P9 325

Settling to

B+ 352
P3 12.2
P7 345
P9 322

That's after about twenty seconds when it all feels quite hot and hummy so I switch off. Volume is at 0. It could be normal hot but I don't know.

Sorry if this is very tedious for you guys, I really appreciate the help.
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Re: new build 36lite with vvr

Post by Bieworm »

Those numbers mean your power tubes are biased at 106.7%. That's not a disaster, but that is also why we generally put a 180R cathode resistor in there. That will drop the bias. We aim for 85%, give or take... 100% is ok, but 85 is better for tube life. It's a cathode biased amp and it's generally accepted that 100% is no problem.
can you make a recording of the process from silent to excessive hum? The hum will decrease when it's biased to 80-90% for sure, but the hum you have may have another cause...making you chase your tail at the power section.
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Re: new build 36lite with vvr

Post by chaliapin »

Thanks bieworm, I'll try to get something and post it, will the numbers look better when I have four tubes?

Can I ask which Ukrainian tube guy you used and I'll order a bunch. There's actually a guy in Ireland selling NOS reflektor military grade but 4 is going to be over a hundred euro and then I'd probably blow one up...
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