So basically a Tonestack placed ahead of a clipping stage would give you more Output Stage Distortion than Pre Amp Distortion, which is probably what I want really. I find you get better clarity with Output Stage Distortion than Pre Amp. Altho I do want to have a Marshally sound so may just keep the tone stack after the gain stages. Pros and Cons.

I did work out the bias of the Pre Amp Valve using a load line and I got 300ohms as the Cathode Resistor! Will probably use split Cathode with 820ohm Resistors on each. If you bias a Pre Amp too cold it can start to sound buzzy I think.

Or there is the original circuit from AX84.com which going by some youtube clips does sound quite JTM45ish which I do like. Only difference being I wouldn't both with a master volume, I prefer just the plain simple Pre Amp Volume.

What is an VDR and what would it do?

Already got an OT in mind, I'm cheating a bit in a way as ampmaker.com sells a Chassis, OT and PT which is perfect for this amp. So a lot of work is done for me already .

Now I've been experimenting on LTSpice with the circuit and as much as I want to keep the Tone Stack inbetween the gain stages, it does have slightly more loss than having it after. Also I've found that the output waveform appears differently for each, I've attached some screenshots of each circuit and their waveforms. Probably wouldn't be much work to swap them around if I changed my mind anyway.

Hello Everyone

Today I started looking at building myself a very small Valve Amp that would give me good tone and distortion, but obviously at a low volume (well lowish ). Anyway I had a look at AX84 and looked at their P1 Extreme. I knew I wanted to use a 6V6 in the Output Stage and a 12AX7 in the Pre Amp so this was a good start.

So I played around with their design and come up with what I've attached. Now pretty much the only things I've changed are moving the Tone Stack to after the first triode, changing the bias of the 2nd triode and lowering the B+ to 250V (should give me 4.5W according to the 6V6 Datasheet).

So what do you guys think? I'm hoping that this will give me nice power amp distortion, however the original design looks like its based on a mix of Pre Amp and Power Amp distortion so not sure if I'll get much distortion until I really turn it up. Also I've never touched a single end amp in my life so I don't know how hard to drive it or anything!

Right, sorry its been a while. Got the Amp powered up, however I had a very low distorted output. Did the battery and neon test on the OT, dead. Checked the Amp with my scope and found the Output was fine until I got to the otherside of the OT. I think my mate fried it when he connected one of the primaries onto the heater supply. So thats the end of that.

Hello everyone! Been a while. I took the amp back off my mate so I could have another look, however I've got to fix an additional mess that he created. Pretty annoyed here. First off, he was getting sparking, this was caused by no solder on the joint of the mains fuse holder, second, hes replaced the rectifier for the heaters with one that doesn't mount to the board so I've got to mount that on the chassis (cant put the old one back as hes broken the tracks) and third he didnt put the nuts back on the pots when testing and this is the amp's only ground points.

A lot of nuts are also now missing, found big blobs of solder on cable cut offs loose underneath the board and the whole thing is covered in cat hair. One is far from impressed!

Hi guys sorry its been so long, been very busy with a new project. My mate wants to look at the amp himself now so I've basically left him to it, I'm not sure what hes done but I don't think he can get sound out of it anymore, he does however now know how to discharge capacitors!

He said the PT looked damaged so I'm guessing thats where the smoke came from, I'll double check for him when I see him. No thanks Roly, that thing is a can of worms!

There isn't much point now am afraid to say as my friend took the amp apart last night to check for cold solder joints and when he put it back together he mixed up a red and black lead. Anyway he said something popped and smoke came out the back, fried PT . I did tell him to wait for me as he didn't know how to discharge capacitors, i told him he was lucky there was no charge left in them!

No I must admit I havent

Right, well its definitely between the EL84s and the OT so that narrows it down a lot. Might take the amp back off him to have another look.

Guys i've had an idea, i think its definitely oscillation like you say as I had the exact same issue yesterday whilst I was experimenting with my 18w (found a coupling cap that I added after a volume control was the cause, removed it and all was well). Now the way I see it this amp used to work, only thing that could have possibly changed were wires. So what about the output phasing? Sure it doesnt have NFB but wouldnt the output phase still make a difference?

O right, in that case i'll just use my Avo in future.

Guys I hate to say it but I've given up. Spoke to my Grandad about it and he agreed its one for Marshall to look at.

Thanks for all your help

No I measured it properly and it was ok, about 6V. What doesn't make sense is when I removed the valves I turned the amp on, checked the heater voltage AFTER the rectifier and got 17VAC and 8.8VDC. When I turned the amp off the AC drained very slowly. What on earth could be storing AC and how is 6VAC turning into 17VAC?! Can't see any issues with the tracks now.