I'm losing my mind

[kerchakone]

Hi, I'm attempting to put together an 18w KLD PVA 18 amp kit and it's not going well.

I have never done anything like this before, building an amp.
The board and potentiometers were pre-built, but nothing else was together.
I have had several issues and I'm not sure if it's effects or causes.

The constant issue is that pin 3 on the El84s keeps seemingly hitting thermal overrun. I have gone through 4 sets of EL84s.

The first issue I had was the paperwork for wiring seemed to be incorrect. The power transformer had a 0v center tap on the 6.3v but the paperwork never mentions it and used 2 100ohm resistors to ground. The voltage was all over the place and those burned up within 30 seconds. I tried to research about the center tap and decided to pull those resistors instead of replacing them and put the center tap 0v to ground instead. Now the heaters have a steady 6.3v.

But now as I said, the cathode bias resistors are melting within 30 seconds. I started to watch the voltage as I powered on and noticed it stayed at 13.6v but as soon as the amp warmed up the voltage starts climbing at an exponential rate.

I decided to increase the resistor from 180ohm up to 236ohm thinking it was too hot biased.
No effect except now voltage starts at 15.5 and starts to climb after warm.

I've changed some wiring from the instructions because it didn't match what I was given:
Paperwork shows only 8/16ohm outputs. I have 4/8/16ohm out.
Paperwork as I said had no PT center tap for 6.3v, so I altered that.
I added a fx loop.
I altered the wiring of the resonance pot since it didn't match the schematic nor make sense to my amateur mind.

Things I've tried and cathode resistors still overrun:
I have disconnected the line from speaker out to the "earth" pot and at the same time disconnected the line from the "sky" pot to the phase inverter.

I've pulled the 12ax7 phase inverter tube.

I've put a patch cable into the return of the fx loop to cut off the preamp.

I don't know if this is an effect or part of the cause or something exclusive but I've had to replace 6 of the 7 potentiometers after they've clearly failed.

I've swapped tubes to brand new ones and the problem seemed to dissappear, but the next time I tried it the heater blew in one.
So i put brand new tubes in again and the problem came back.

My first set of tubes (JJ) were damaged by the heater circuit issue with the incorrect PT wiring. pins 4/5 shorted to pin 3.

Second set of tubes (JJ) also were seemingily damaged by the issue prior to fixing it. (don't remember exactly, this has been a 2 week mess). but these overheated cathode resistors.

Third set of tubes (JJ) seemed to work couldn't see any issues, but I had a bad volume pot. Replaced the volume pot and immediately the one tube heater blew up.

4th set of tubes (PSVANE) are back to overheating the cathode resistors.

Is it possible I need a 5th set of tubes as the PSVANE tubes were bad from the getgo?

I checked voltages with the voltage map they give and they seemed "close enough" to me. But recently I found that the "sky" pot v reading on the board is reading over 30v and it's supposed to be only be 11v. Other than that everything seems fine.

Sorry for the novel, with as long as this is I know I've left out a ton of things i've done or tried or measured.

Please help!

[kerchakone]

http://www.kldguitar.com/Home/Product/PVA18

Scroll down and click documents tab, and there's all the paperwork.

[kerchakone]

I've also tried both pentode and triode mode.

The problem occurs while in standby since it still allows the high voltage through circuit. So I eliminated the "standby" altogether.

Also if I pull either el84 it still overheats. Doesn't seem to matter which socket.

No 12ax7 has blown yet. They seem perfectly fine.

Pin 2 shows 0v most of the time but swings negative and very slightly positive voltage. I know that positive V is not right, but have seen that that can happen with some tubes.

Pin 9 shows 368v not 360v. I don't know if that's an issue, I assume no.

Could pin 2 behavior actually show that the bulbs are indeed defective from the factory?

[Bieworm]

Djeeez man! That is an overly populated circuit. Apart from the fact that this is no beginners amp build, I think it has a lot of obsolete components and I can’t imagine why the creator did this.
There’s a lot of simpler plexi schematics out there than this one.
I advise you to put it aside and start with a starter build. The 18W lite2b for example.
Can you post some pics of your build?

[AussieTim]

I would seriously just write this one of as an experience
There are several reputable kits on the market although the mojotone one doesn't get a lot of love on this site.
Depending on what is salvageable you could BYO by buying a decent mainboard and using your existing chassis, I would probably get the transformers checked out and replace them with some good ones, brand preferences and your location will play a part in determining this.
Not getting too fancy on your first build is a good idea we all want to put all the bells and whistles on our builds, but learn to walk before you run.
Something like a (mumbling up my sleeve here) Fender 5E3 is a great first build or a simple version of the 18 watt
I came from having virtually no electrical knowledge to having completed a few amps now and the help I got from the guys on this site has been fantastic and have learned lots along the way,
I have never had the issues you have and frankly, they sound scary which is why I encourage to just sideline this amp and build something that is tried and true, building amps is a great hobby and I love hearing them and about building them and wish you success
Tim

[kerchakone]

I figured it out. The paperwork was incorrect about the transformers. There was no other issue in the end.

The amp sounds absolutely awesome.
I have since modified it to have 6 different preamp tones. Plexi/jcm/silver jubilee/bassman/fender/vox.

I’ve also added clipping diodes soft and hard to play with. Have several other planned features.

[Daviedawg]

Well done persevering to solve the issue. But as was said in the comments this was not an easy build. On the plus side you will have learned a lot in the process.

Dd