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Just finished building my kit this weekend.

But I'm troubleshooting a voltage issue and I'm stumped...
Most of my voltages are good but a few are out of whack in my pre-amp section and I cant seem to nail down why...
Working my way across the board.
V4 pin 8 (and V3 pin 8) are 21 spec is 22
B+ to OT is 364 spec is 360/400
V4 pin 4 (and V3 pin 4) are 328 spec is 348
The next pin (that powers the resistors to the pre-amp plates) is 254 spec is 255. It also tests 254 at each of the resistor junctions
V2 pin 8 is 49 spec is 50
V2 pin 7 is 3.2 spec is 18
V2 pin 6 is 198 spec is 204
V2 pin 1 is 158 spec is 158
V2 pin 3 is 1.2 spec is 1.4
V1 pin 1 is 97 spec is 130
V1 pin 6 is 230 spec is 130
V1 pin 3 (and 8) is 1.2 spec is 2.0

I've done a bunch of checking, resistors all seem right - the 100K plate resistors on V1 are a little high but under 110K.
I reflowed several connections - no change.
I've pulled pre-amp tubes and checked continuity to each socket pin - all good.
Double checked the V1 jumper - fine.

Im not a tube expert but the V1 plate voltages are baffling me. How do I have a common voltage on one side of 2 equal resistors but a different voltage on the other side? Or am I picturing this flowing backwards?
Please help - what do I need to check, where's my problem?

Attaching a photo of my build and the pre-amp area.

Worth noting that I have prepped for a VRM, so I have installed .1uF filter caps and relocated the 1M input resistors directly to V1.

Different voltages can be caused by different tubes or issues within tubes or poor connections. Check connections, swap tubes etc. One stp ata time.

Is the amp working otherwise?

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Thanks Stephen,
I did plug a guitar in and it plays, but the tone is fairly clean and if I turn up the Normal Channel volume I start to get clipping that's almost Tremelo like (especially if I'm plugged into the Bright Channel Hi). I assume it's the Normal channel side of V1 with the higher plate voltage and thus the clipping...?

I did try swapping V1 and V2 last night as you had suggested.
The voltages were mostly different but it still appeared there was a bias between the V1 plate voltages. I didn't record them though - I can do it again and record them if that would help diagnose.

I'm fairly new to this, so I don't really have spare tubes kicking around. I do have a 12AX7 I could swap in, but it came as a swap out from another amp so I'm not even sure if it's known good... or just swap it into V1 and see if the plate voltages even out?

I am totally stumped.
Removed V1, reflowed all the connections.
Used a small screwdriver to 'tighten' all the sockets (a recommendation I found elsewhere).
Replaced V1 same voltages at the plates.

Found a 12AX7 that I had around and swapped it with the 12AY7 in V1.
The V1 plates voltages were up to 238 (pin 6) and 142 (pin 1)
V1 pins 3 & 8 dropped to 0.9
V2 pin 7 was at 3.3
Other voltages with still within reasonable range.

Swapped the 2 - 12AX7s, only slight differences.

To me this implies the tubes are all good but still some other issue...?

Tubes do look good. The only thing left really is the resistor feeding it. I guess you could swap them and see what happens, unless you have a replacement. Or swap the leads on the boards to the plates and see if the problem follows the lead or not. to isolate it to the resistors.
Rare but possible, defective or leaky tube socket? Check socket voltage to ground in that area, should be zero

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Thanks
That is excellent advice - I don't know why I didn't think of that.

Ok... so I swapped the plate leads and the voltage skew followed.
I think that implies the resistors are ok, no?

I'm not sure exactly where to check the tube socket, but I can't find any voltage prodding around on/near it...

Now what?

If the skew stays with the lead, that means the problem is the resistor. To really be sure. Swap the resistors! This is a rare issue by the way.
You can also pull the tube and see how the voltages measure, but with no current flowing it may not make a difference..

Put the voltage probe on the socket, and the negative lead on the chassis. See if there is any voltage measured.

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

So I swapped the 100K resistors and the voltages stayed the same.
Voltage skew followed the plate leads but not the resistor.

Pulled V1 measured voltage on the sockets - pin 1 and pin 6 both showing about 260v (measures the same on the board) with no tube.

So it's not the resistor. Is the plate lead flaky? Just attach a jumper between the socket pin and resistor or measure the resistance of the lead while moving it.

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Not sure I understand...
V1 removed...? Resistance between plate socket and lead of the 100K resistor while moving the wire that actually connects them?
Just looking for it to fluctuate?

Just trying to eliminate the lead as a problem.

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

From the board eyelets to the tube's plate sockets I get ~9 ohms and ~11 ohms. The higher resistance is a slightly longer lead.

A couple of other observations that I thought might be worth pointing out...
When I had the 100K resistors out while swapping them I did check them quickly.
They were both a bit on the high side. One was about 107K but I did notice that as I held my probe on the other it was slowly creeping higher I finally stopped at about 112K. Is this a known failure mode of Carbon Comp resistors? And would this be amplified with high voltage/current? Starting to wonder, if this resistance rose significantly under power/load, would that throw the voltage?

The other observation I had was with the signal leads removed, the tube in place and power on I was getting ~9 volt reading from the grid pin on the triode with the higher plate voltage, while almost no voltage on the lower voltage triode grid pin. I'm not sure if this is a cause or effect thing but found it interesting so I thought I would mention.

Thanks for all your help Stephen

The resistance should really be zero in both cases. I suspect it is but maybe your meter cant measure that accurately.
We can send two matching resistors or go to carbon film. CC do change a bit under higher voltage but this is about 10% and I think the voltages are off more than that. Maybe a new socket too.
Apart from that, There isnt much else left.

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

My meter is not a Fluke or anything like that - it's pretty cheap, going in I thought it would suffice for this project.

As for next course of action - I'm good with whatever you recommend.
Like you, my gut seems to say resistors or socket but I haven't really been able to provide scientific evidence that either is bad... you have wayyyy more experience at this than me, so I'm good with whatever your recommendation is on next steps.

As a side note - I have learned a ton about this circuit and these types of circuits through this exercise.

Thank you for the great support Stephen!

Ok, I received the parts you sent Stephen - Thank you very much.
I have installed the replacement V1 socket and it looks like we've solved the issue with V1.
Unfortunately it looks like I still have an issue with the voltage at V2 pin 7.
Here's a refresher of my initial voltages

Here's my voltages after replacing the V1 socket (only the socket, I didn't replace the plate resistors at this point)
V4 pin 8 (and V3 pin 8) are 20.6 spec is 22
B+ to OT is 362 spec is 360/400
V4 pin 4 (and V3 pin 4) are 322 spec is 348
The next pin (that powers the resistors to the pre-amp plates) is 234 spec is 255.
V2 pin 8 is 44.6 spec is 50
V2 pin 7 is 2.9 spec is 18
V2 pin 6 is 181.5 spec is 204
V2 pin 1 is 143.5 spec is 158
V2 pin 3 is 1.1 spec is 1.4
V1 pin 1 is 114.7 spec is 130
V1 pin 6 is 109.0 spec is 130
V1 pin 3 (and 8) is 1.9 spec is 2.0

V2 pin 7 was an issue before and still appears to be an issue...
I notice my voltages are all slightly on the low side, although my B+ is almost right on (@362)
So what's happening now?
To get started, since I do have a spare 12AX7 I swapped it but saw no significant differences.
I did some basic checks of resistance values and continuity and don't see anything obviously out of whack.
What's next? I feel so close but so far...

Also, I did plug in for a few minutes... haven't played a 5E3 before but thinking it's cleaner than it should be (based on clips I've seen) and quieter than I expected (based on what I've read).

It could be that R10 is larger value than spec. This would clean the amp up a bit. Tweed starts to break up around 4 on the dial. Some poeple prefer it to be cleaner though.

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Thanks Stephen.
You know what, I think it was just me... I took it off my bench and set up the speaker a little better and really spent some time playing with the settings and playing through both my Fender and my Gibson and pushing my attack a little more.
I think I'm finally getting a knack for the controls and really digging the tone - even the Gibson (LP Std) sounds way better than I thought it was going to (from what I had read) with this amp. And my wife thinks it's plenty loud now... which I guess means the VRM will have been a good choice.
By the way R10 measured right at 56K.
Quick question - is there a reason my V2 pin 7 reads so low or is it just the way I'm measuring it?

Thanks for all your help and support through this adventure Stephen - so glad that I purchased from someone that would support me. Plus I've learned a TON about this amp in the process.
Eager for the VRM (or at least my wife is) and I think I'm going to try the cathodyne smoothing resistor to see if it will sweeten up the LP even more.

Yes, waiting for the VRM boards has been painful. Almost 5 weeks in transit so far. Do try the smoothing resistor. Every tube is different and that usually accounts for votage differences. Add in carbon comp resistors and that adds more flavour.
Bottom line is that you like the amp and that you enjoyed the build!

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Yes, agreed and agreed.
I'm sure that I will find myself addicted now... tinkering and tweaking my set up perpetually.
Who knows at some point I will be picking out my next kit too

Thanks Stephen!