12AX7 Distance

[Littlewyan]

How close can you have two 12AX7s and a 6V6 do you think? Its just I want to build an amp into a small chassis and may want to add a cathode followerer (2nd valve). Heres a link to the chassis, looks like it can only really go inbetween the two valves currently there. Heat might be an issue though.....

http://www.ampmaker.com/store/Punched-c ... d-1x9.html

[Stevem]

No more than 2 inches, that way you can use a big bottle tube like a kt88 or 6550 if your power transformer has the added heater and main secondary current.

[Littlewyan]

I'll have to forget the 2nd Pre Amp Valve then. Only wanted it for a Cathode Follower but the chassis is just too small.

Has anyone had any experience with the P1 Ex?

[Phil_S]

You seem to be on the UK/Euro side of the pond, so I'll try for metric dimensions. It looks to me like the typical octal socket will require about 48mm with the mounting ears and the typcial noval socket will require about 33 or 34mm with the mounting ears. Remember, the ears extend slightly beyond the screw holes.

Visually, it looks to me like you can shoehorn in another noval socket on that chassis, but you will need to measure it. If you do that, as Stevem notes, you will not be able to use any big coke bottle tubes. However a straight sided 6V6 or 6L6 should fit and it should not cause any cross talk above the chassis. It will be crowed on the underside. With careful lead dress, you can make it work.

[Littlewyan]

Yer it may not be worth it. I wanted the Cathode Follower for the Tone Stack, but where I will have a lot less insertion loss through the Tone I could be asking for trouble on the lead dress side. I'm just trying to build a small amp for a low cost and if I start to look at larger chassis' and larger head cabinet the cost goes up by £40 straight away. Not to mention I'll have to then use a different faceplate etc.

[matt h]

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[Littlewyan]

Good idea Matt H, I suppose using a Transistor as just a Cathode Follower wouldn't have any affect on Tone. Would you agree?

[Stevem]

you could concider using octal like the 6SL7 which you could set up just about the gm of the ax7 and is far higher current output will ya real close to the drive of a cathode follower, but without the low impeadance or course.
But heck I have heard some cathode drivin tone stacks that sounded better when put back to being fed off the plate.
I do not think that by any means its cut in stone that a cathode follower sounds best.

[Littlewyan]

No I only wanted a Cathode Follower to lower the insertion loss so I can push the Output Valve harder. I'm pretty much limited to a single Noval and Single Octal in the Chassis I'm using, so I'm trying to make the most of it and get as much overdrive as possible. Won't be near a Trainwreck but hopefully at least a Marshall Plexi. The circuit I'm using is a P1 Extreme BTW.

[matt h]

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[Littlewyan]

The only main difference between my P1 Ex and the Std P1 Ex is mine will be running at 250V B+ with a 6V6. Also using an SF will allow me to adjust the Tone Stack if needed. I found that if I change the current tone stack closer to a Plexi Stack I just lose more signal. With an SF I will still retain more signal than the original without an SF.

[Phil_S]

I think you are too concerned about signal loss. Gain > TS > Gain > Power.
It will work like a "champ."

[matt h]

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[Littlewyan]

I've checked the biasing of all valves, the only one that may need adjusting was the 6v6, but we'll see once its built. Also its no big deal adding the IRF820 in as a source follower, if I don't like it its easy to take out. Looking at other possible MOSFETs atm tho as this one isnt insulated. Could cover it with heatshrink but it'd be nicer if I had an insulated case.

[Stevem]

You will never get the true cranked plexi crunch with its high order harmonic distortion from a single ended amp, end of story!!