B'Day Amp Build

[raulduke]

r.e. upping R6 to 1M I don't think that would be a good idea!

I think it may well decrease the gain, and could cause biasing problems and other issues.

If you want even more gain, another cap in parallel with C3 would do the trick.

Make sure the caps are rated at the right voltage too (at least 25V).

Also, be safe... messing with valve amps can be deadly!

[Willholmania]

Really? It was suggested to me by a guy I know who works as an electronics engineer at the BBC. He's normally spot on with his electronics but he did say his valve amp knowledge is rusty!

[raulduke]

Well I'm by no means an expert but I'm pretty sure changing the 820R at R6 to 1M would not be a good idea  !

The notes here:http://www.ampmaker.com/infocentre/thread-2.html for modding the WF55 on Ampmaker apply pretty much equally to the Se5a, and decreasing the equivalent of R6 on the WF55 is suggested for more gain.

I would try the extra cap on V1a first as suggested. If that isn't enough, tweak the cap on V1b.

These are both relatively simple mods as you can 'piggyback' the new caps on C1 and C3 in the schematic posted.

There will be a limit on how much gain is possible with the circuit anyhow; there are only two gain stages.

An alternative, rather than modding the amp, a really easy solution is to use a booster (ZVex SHO etc.) to push the preamp valves into distortion.

[stevewire]

raulduke,
Totally awesome!!!

[jimilee]

Man, that is fantastic! And yeah, Happy Birthday mang!

[Guitarmageddon]

Geez, I missed this.
Gorgeous amp, congrats. What a great birthday.

[Willholmania]

Thanks Raulduke - much appreciated. I hadn't seen that WF55 stuff - very handy. I'll try that cap today and report back. I had considered adding another gain stage, which is where I may end up.

[Willholmania]

Right. Tried the 25uf cap across C1. Not a mod I'd recommend as the results are either impossible to hear ro extremely subtle.

Looks like I'll have to go for an extra gain stage, a la the AX84 High Octane circuit.

[hylandren]

 Wow, what incredibly clean guts!
Beautiful inside and out.

[Willholmania]

After the unsuccessful 22uf cap experiment I fitted a VVR circuit today (from Hall Amplification via Barry at Amp Maker). This works very well from, about 4 on the pot up to flat out (when it's no longer doing anything). A very good 20 quids' worth.