1987X reissue issues......

[TheDirewolf]

First time posting here fellas but I've been roaming the halls for quite some time. I'll keep the back story short. I bought a 1987XL 2004 model about 6 months ago. It was modded by a well known amp modifier/builder. I replaced the stock Dagnall's with Classic Tone all throughout and removed all of the mods to return to stock. Sounded great but was wanting to try a few mods. Long story short, I ended up on Valvestorm and gutted the entire amp. It now has a PTP board with PEC pots, belton sockets, and a new wiring kit. Finished it all up and got to the testing phase of the 50 watt Metro Kit instructions and it's been all down hill from there.

V1 pin1 154vdc. pin3 1vdc. pins4&5 3.5 vac pin6 135vdc. pin8 1.4vdc. pin93.5ac

V2 pin1 167vdc. pin3 1.1vdc. pins4&5 3.5vac. pin6 300vdc. pin8169vdc. pin9 3.5vac

V3. pin1 228vdc. pin3 42vdc. pins4&5 3.5vac. pin6 223vdc. pin8 42vdc. pin9 3.5vac

V4. pin2 3.5vac. pin3 511vdc pin4 510vdc pin5 -47vdc pin6 511vdc pin7 3.5vac



V5 is all the same as V4.
I had preamp tubes in it but no power tubes. The bridge + also measured 512vdc and the PT high voltage secondaries read 366 vac each. Keep in mind the amp and new transformers all worked fine until I gutted the amp. It also has a Lar/Mar PPIMV that I installed prior to this "upgrade" that worked flawlessly as well. I have pictures that I will try to get uploaded ASAP. Any and all advice and or help is greatly appreciated.

I was hoping my first build was gonna go off without a hitch but no such luck.

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[TheDirewolf]

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I hope this works. I also forgot to include some information. Guess my ADD kicked in. I did put a set of Groove Tube EL34M's in it and they immediately red plated. I tried swapping out the 47K bias resistor for a 56K and it made no difference. I also tried to take readings on the preamp sockets with no tubes in. I measured 508vdc on V1 pin 1 and quickly shut the amp down. I haven't and won't power it back up until I get some advice. On a positive note, the amp sounded really good until the board swap. The Classic Tone tranny's were a HUGE step up in tone from the stock Dagnall's. I just couldn't leave well enough alone. Doh!

[Tone Slinger]

Check that the grounds are all good. Check the bias circuit, rectifier diodes. Maybe a tube socket is bad ? Hopefully Neikeel will chime in soon.

[neikeel]

I think the above advice is good, check that your bias caps and pot are grounded to a proper star ground and the nuts are sufficiently tight to dig into the chassis a little. I use a dedicated black wire under the board to one of the output tube ground lugs.

Without the power tubes in does moving the bias pot vary the voltage you are seeing on pin 5 of your output tubes?

Check the shield on your PPIMV pot is not touching the back of the pot (ideally shrinkwrap it) as it is 'live'.

If that does not help post some more pics of the output tubes and selectors.

Also we will have to take your word about all of the board hook ups (I usually strongly urge new builders to put the off board hook up wires up through the holes next to the turrets, like post 68 amps so that you can trouble shoot more easily.

[TheDirewolf]

First and foremost thank you for taking the time to look at my pics and offer up your help.

Adjusting the bias pot DOES change the -vdc reading for pin 5.
I did go through and check and recheck all the grounds and even lifted the board to retouch all the ground wires underneath. I actually considered running the off board wires up through the perforated holes but my pride got the better of me. Wish I had done otherwise now.
The PPIMV shield wires are not in contact with anything other than the designated lug.
I also contacted Magnetic Components to verify that my tranny hook ups were indeed correct done and the nice folks there let me know I did it right.
I'm going to take my readings again and see what I come up with. Thanks again for the help! GREATLY appreciated.

[danman]

Is the only issue you are having is that the power tubes are redplating? You measured -47vdc on pin 5 of each power tube socket which is good. Like neikeel mentioned, you should see that negative voltage change when you turn the bias pot. Set the pot for the most negative voltage before powering the amp up with power tubes again. Are you certain that the power tubes are a good working pair? If they redplate again with the bias voltage turned up, its possible that it could be caused by oscillation in the circuit.

[TheDirewolf]

Ok. After checking grounds and solder joints under the board I fired up the amp and took readings again. All of my numbers are pretty much the same. I have noticed that if I ground both leads to the chassis I show .003vac on my meter. My + side of the bridge rectifier is still showing 512vdc and the AC sides are showing 366vac each. I haven't put any power tubes in yet. I guess my main concern is that my numbers are much higher than that of the kit instructions. Is this normal? I know B+ will fluctuate with different PT's.

The GTEL34M's I had weren't new but they weren't bad either. The EHX EL34's however were brand new and I cannot get the bias low enough to use them. I bumped the bias resistor up to a 68K even and still no luck.

I did read the pot side of the 220K bias input resistor and it had 366vac. The other side had 219vac. The negative side of the diode reads -58 vdc.

Everything seem ok so far number wise to try my last set of known working Svetlana EL34's?

[danman]

Voltages seem a touch high but they will come down when the power tubes are inserted and biased up. You may also have a slightly higher wall voltage that is causing this. What are you showing at your wall outlet? I would set the bias voltage to the highest point and insert power tubes. Let us know what your readings are on pins 3 and 4 with the tubes installed and whether you are still seeing any signs of redplating.

[TheDirewolf]

I'm seeing 124-126 at the wall. I'll put some tubes in it and see how it goes. Thanks for putting in the time with me on this. I'll report back soon.

[TheDirewolf]

Well. So far so good my trusty old Svetlana's are NOT red plating at idle. I'm currently (pun intended?) looking at 30mA on my bias meter and -43vdc on both pins 5. Both pins 3 are at 486 vdc. Still seems high to me. Is this normal for the 40-18023 ClassicTone PT? I'm running 50/50 mains, 32/32 screens and PI, and 16/16 preamp. I'll let it settle for a while and if all is still going well I'll hit the front end with the Les Paul and see how it holds up.

THANK YOU. THANK YOU. THANK YOU Neil and Dan for your time and patience. You guys rock!

[syscokid]

I think those voltages are still a bit high. I'm not sure what the ratio of increase could be with those higher wall voltages. That PT should be putting out about 450vdc. Can you check the readings at the Rectifiers + terminal when operating in the Standby position with no tubes installed? Should be about 350vdc.

[TheDirewolf]

I'll check it in a few. Be right back.

[TheDirewolf]

Sorry for the delay. I had a hard time putting the guitar down. So the positive terminal on the bridge rectifier in standby with no tubes reads 331vdc. Is the high voltage the reason my preamp tubes get about as hot as my power tubes?

[danman]

Hows the battery in your meter? I have had high readings before that were caused by a weak battery. I have that same PT and it should be down around 440-450vdc at the plates. Are your heater filament voltages pretty close to spec?

[TheDirewolf]

Batteries are pretty fresh and heaters are at 3.5vac. I thought they were supposed to be around 3.15?