Yellow Paper Mod - VTA M125s - did it help my situation?

[gadget73]

kind of a messy amp inside. Lots of wires running around in a fairly tight area. I can certainly see possibilities of coupling between things that shouldn't be coupled between. In OP's amp I see a few questionable solder joints and some melted wire insulation which probably isn't helping matters either.

Looks like the resistors going to the terminal strips in the middle of it all are from the plates, and I assume the wiring runs to a triode/UL switch which would flip the screen connection around. Honestly I'd dump that entire mess and wire it for whatever mode its going to run in. Eliminate the wire runs and possibility of things going funny from it.

 

[whoaru99]

Thank you.

With all the advice so far and some stuff I've done last weekend (ordered parts):
- I'm replacing all the tube sockets - I have 10 on order.
- I've ordered the various resistors that are soldered onto the tube sockets - so that I can start fresh.
- This amp has a lot of exposed leads so I've ordered teflon spaghetti stuff to cover the exposed leads on the new resistors etc that I will be installing.
- I've ordered new 20 AGW solid core tinned copper wire and some braided wire to replace any poorly done wiring that was done.
- I'm on the fence regarding the autobias boards but I'm seriously considering them and now would be a great time.

So I will clean it up well and likely run it buy a local shop that repairs stereo equipment has a decent local reputation see if the can scope it etc after all my repairs are done.

This is a gut shot of how it looked at the time I was chop stick testing it:

Thanks again everyone for your terrific ideas!

Looks like plenty of sketchy solder joint just in what I can see from my smartphone screen.

 

[FlaCharlie]

I'm replacing all the tube sockets - I have 10 on order.

Why on earth would you do that?

I've only had to replace a few sockets over the past 20 years - mostly on vintage gear that's 60 years old or so - but never replaced more than one in any particular amp. They were replaced because a contacts either broke off or couldn't be tightened enough to make a tight connection with the tube pins.

The most recent incident involved electrical leakage between pins of a NOS Cinch loctal socket. In that case I was converting from octal output tubes (6V6s) to loctals (Russian 4P1Ls) and got wacky voltages on one. As a last resort I replaced the socket and that solved the issue. Luckily, I had purchased 5 of them.

I would think that a kit that cost thousands of dollars would come with reasonably decent tube sockets.

 

[BNR_1]

KT88 - is the black wire exposed from melted insulation? This is the wire that goes to the neg terminal for the speaker. Hard to see from the photo.

 

[KT88Lvr]

Very good! One suggestion. For those resistors and cap attached to the sockets, keep the socket-side lead as short as possible. Even a 1/4-inch lead can have enough capacitance to affect the stability of a borderline portion of the circuit. 3:27 of video shows resistor lengths staggered to keep length to socket as short as possible.

Neatness counts and can help instabilities issues due to EMF coupling of signal lines. Good luck with the fix!

View attachment 2464770
View attachment 2464771

Thank you!

 

[KT88Lvr]

Why on earth would you do that?

I've only had to replace a few sockets over the past 20 years - mostly on vintage gear that's 60 years old or so - but never replaced more than one in any particular amp. They were replaced because a contacts either broke off or couldn't be tightened enough to make a tight connection with the tube pins.

The most recent incident involved electrical leakage between pins of a NOS Cinch loctal socket. In that case I was converting from octal output tubes (6V6s) to loctals (Russian 4P1Ls) and got wacky voltages on one. As a last resort I replaced the socket and that solved the issue. Luckily, I had purchased 5 of them.

I would think that a kit that cost thousands of dollars would come with reasonably decent tube sockets.

Thanks - I've always wanted to clean them up - they are a bit of a mess - and it shouldn't be too difficult as I've already built them once. It is funny - you start out "this is going to be the neatest, cleanest looking wiring" then as you get further along in the directions - "what the heck happened here??"

Anyhow - I'd like to do it better and investigate it as this amp is much less stable than the other amp.

 

[KT88Lvr]

KT88 - is the black wire exposed from melted insulation? This is the wire that goes to the neg terminal for the speaker. Hard to see from the photo.

Thanks for looking - noticing. From what I recall I think the iron burnt some of the insulation on accident - and I covered it poorly in shrink tube - at the time I used a match for the shrink tube after watching my dad do it with his heathkits - always came out awful for me. I have a nice heat gun that does a much better job. So one more thing to fix.

 

[KT88Lvr]

kind of a messy amp inside. Lots of wires running around in a fairly tight area. I can certainly see possibilities of coupling between things that shouldn't be coupled between. In OP's amp I see a few questionable solder joints and some melted wire insulation which probably isn't helping matters either.

Looks like the resistors going to the terminal strips in the middle of it all are from the plates, and I assume the wiring runs to a triode/UL switch which would flip the screen connection around. Honestly I'd dump that entire mess and wire it for whatever mode its going to run in. Eliminate the wire runs and possibility of things going funny from it.

Thanks - I was considering that - as I only run it in the UL mode from what I recall - I was never happy with the other mode. I should be able to figure that out.

 

[KT88Lvr]

That all sounds great but be prepared to do a lot of work and possibly see no change. My amps are a completely different build as we are dealing with kits, yet they used to exhibit identical behavior. To me that implies an inhernet design weakness, versus workmanship. Having said that with the extent of what you are planning slipping in AB boards would be a no brainer, most of the wires run over to the sockets. To illustrate:

View attachment 2464752

Thanks and agreed - Bob could have done a much better design - I remember being super frustrated with the tight confines. Those two big fat blue caps in the middle were a real joy to deal with. I'm real envious of those eyelet boards above.

 

[KT88Lvr]

Looks like plenty of sketchy solder joint just in what I can see from my smartphone screen.

Yeah I was dealing with one of those Radio Shake 25.00 solder irons - my Hakko is much easier to use and deal with - I should be able to reheat them with some flux and make them nicer. I'll gut it and go from there.

 

[FlaCharlie]

Thanks - I've always wanted to clean them up - they are a bit of a mess - and it shouldn't be too difficult as I've already built them once. It is funny - you start out "this is going to be the neatest, cleanest looking wiring" then as you get further along in the directions - "what the heck happened here??"

Anyhow - I'd like to do it better and investigate it as this amp is much less stable than the other amp.

It's not necessary to replace the sockets in order to improve messy wiring or redo sketchy solder joints. Just de-solder everything, remove excess solder using de-soldering braid and clean the pins up with a wire brush.

 

[whoaru99]

Yeah, certainly not necessary. But, IMO, depends on the extent it's going to be rewired or whatever. It might be less cost if one considers anything for their labor to snip them out and replace rather than try to rescue them.

 

[gadget73]

also depends on the quality and condition of the sockets to begin with.

 

[KT88Lvr]

The sockets where super cheap - I bought the same brand sockets from PartsExpress as VTA provides:

055-512 8-Pin Tube Socket Celanex Drop-In for Fender 10 EA $0.95 $9.50

The keyslot was worn in one of the rectifier sockets and I over heated some of the leads in the others. Hopefully when these arrive they will be the same and same quality.

Removing should really open up the area for closer examination.

Thanks again!

 

[BNR_1]

Hi KT88 - take your time for addressing your issues. You may not need to replace all 10 sockets as others suggested. I know you have already placed your order on your sockets. Should be good. Another good selection of sockets are the Belton Micalex sockets. Keep us up to date on your progress. Regards

 

[KT88Lvr]

Hi KT88 - take your time for addressing your issues. You may not need to replace all 10 sockets as others suggested. I know you have already placed your order on your sockets. Should be good. Another good selection of sockets are the Belton Micalex sockets. Keep us up to date on your progress. Regards

Thanks very much BNR.

 

[KT88Lvr]

We'll the tube sockets came today - thank goodness they were cheap - because they are top mount vs bottom mount - so I'm out 10 bucks. Not really worth it to send back.

Looking at the amp guts - I'm thinking there isn't much I can do to neaten it up and provide for better wire routing - I was scratching my head - then when I touched a wire connecting to the quad cap - I found it completely loose - and not soldered in - so I'm super glad I found that.

I think I'll just reflow most of the poor solder connections. The transformer leads are all too short to reroute so just replacing the sockets and rewiring those are not going to allow me nice routing of wiring - it is always going to be a bit of a rats nest.

Anyhow - my initial observations.

I'll think more on it. Glad I found the loose connection.

 

[Lavane]

Maybe top mount isn't a bad idea? The heads of the screws sent with the VTA amp kits sit a bit high. The base of the power tubes tend to sit on them. S9me people add small felt pads around the sockets to clear them. The metal mounting ring of the top mounts holding the socket itself should be high enough to clear the screw heads. Just a thought.

 

[KT88Lvr]

Maybe top mount isn't a bad idea? The heads of the screws sent with the VTA amp kits sit a bit high. The base of the power tubes tend to sit on them. S9me people add small felt pads around the sockets to clear them. The metal mounting ring of the top mounts holding the socket itself should be high enough to clear the screw heads. Just a thought.

Thanks - I did order a few of the bottom mounts in case I do want to replace one or two. But I'll see how the top mount works.

 

[KT88Lvr]

In for a penny...

After finding that loose wire coming off the choke to the quad cap - I decided to gut it. So it begins.

So far while digging in I found:
- Loose wire from choke - already mentioned.
- Speaker ground wire connection to speaker connector - very weak to the point of breaking. I recall that was a pain to wire as they were super close to the transformer.
- Wire between two tube sockets - just broke when I touched it very weak I guess from bending ore movement - just broke.
- Terminal strip looks pretty poor with some discoloration.

The tube sockets top mount should work out just fine - thanks @Lavane

Pictures of where I'm at - demo stage:

Top mount tube socket - should be fine.

Quad cap black wire on bottom top - not soldered or solder broken - just moves in lead.

This guy looks bad.

Different angle.