Hammond ao-35 conversion

[Slimtim]

Well i'm finally getting around to doing this.Tubes should be here monday i hope.i'm using this man's conversionhttps://www.youtube.com/watch?v=GVLRmCbPfbs as a starting place.But i'm going to try the 18 watt marshall volume and tone instead of the moonlight but only because i have those pots here.And here is a link to those circuits http://amps.zugster.net/articles/tone-stacks But what voltage caps should be used on the volume and tone?i have 2 .01 disk shaped caps and one is 20% larger than the other but i don't know if they're right voltage ratings.At this small does it matter?

[plexi50]

The cap value is not as important as the voltage it is rated for. Most all amplifier coupling and tone capacitors are rated between 400VDC-600VDC.

[Slimtim]

mine don't say so how do i know?also on the resistors,if i don't have the exact res. called for i can stack a couple end to end to add up to the res right?

[John]

mine don't say so how do i know?also on the resistors,if i don't have the exact res. called for i can stack a couple end to end to add up to the res right?

Normally, the disc cap are ceramic, and *usually* are at least 600v rating. And yep, resistors in series add up.

[Slimtim]

Cool thx.I have all the holes drilled just need to wire it all up.Very simple little amp to convert.i really like the small size of it.It's as small as i've seen for the output it has.How high amp should my fuse be?I bet this 1 amp i have isn't going to cut it is it?Here is a link to the ao-35 schem http://www.captain-foldback.com/Hammond_sub/schematics/AO35.JPG

[daven]

I've used a 1A fuse* for an AO-35 to carmen ghia clone conversion (as well as a couple of AO-39 to matchless lightning conversions) without issue.

*I actually used some slo-blo circuit breakers--something maybe doug can consider stocking.  I prefer them for for new builds, and have confirmation that they work as advertised (courtesy of a failed-short 1N4007).

[Slimtim]

Well thx all for the help.It's not done yet but it is up and going and i'm very pleased with the results this far.i'm very surprised at how little hum or noise it's putting out given it's age and my half assed wiring and soldering work.Even with single coils it's very quiet.This is my first working guitar tube amp and i think it's a hell of a start.Now to finish it up and build a head or combo for it.

[Slimtim]

Well i thought all was well.With a 12ax7 in v1 and 1 on phase inverter i get a high pitched squeeling noise from 6-8 on the volume,1-5 and 9-10 sound fine.With a 12au7 in as phase inverter all is well no squeel at all from 1-10.If i put a 12au7 in v1 and a 12ax7 at p.i. the squell is only at about 6-7.I put in new pots and rewired the volune and tone but that's not it.So is my gain too much with 12ax7 in v1 and v2?

[silverfox]

It could be feed back from the power stage at a particular favourable frequency. You might try a simple solution first. If you have a metal tube shield for the 12AX7 phase inverter, try putting that over the tube. This looks like a compact design and you might be getting feedback from the power section.

Silverfox.

[Slimtim]

nope still there.also it will also squeel rather a guitar is plugged in or not.Would upping the resistor value to the grid on v1 help.i notice on the dr z carmen ghia it has a 68k there where i have 33k.I have a single input with a meg across it.

[Platefire]

You may need to swap the power tube wires to plates from OT if you have NFB hooked up. Platefire

[Slimtim]

i don't know what you mean,which wires exactly do i switch?If nfb is present on a stock ao-35 then it's still hooked up on this one cause i didn't undo it.

[Slimtim]

ok i see what you're saying just swap one for the other going to pin 7 on the power tubes from the ot.But is there a way to check if that needs to be done without actually doing it?Because this amp is little and that area is tight as hell for me to work on.Also would that be the issue if it only squeels at a certain volume and only with a 12ax7 in v2?

[Slimtim]

Is there any chance shielded cable on the input,volume and tone will stop this squeeling?My input,volume and tone are mounted right under the ot.I went ahead and converted my roommates ao-35 the same way and his is doing it too,but even worse.

[PRR]

> My input,volume and tone are mounted right under the ot.

VERY bad plan.

You need 0.05V at volume pot to make full signal. There's 300V on the OT plate leads.

Doesn't take much stray leakage from 300V to make 0.05V on these high impedance tone/volume points.

Shielding may help but IMHO you need to get these low-level and high-level wires FAR apart.

[Slimtim]

Thx prr.Moved the input back to it's factory location and rerouted the volume and tone wires and the squeel is all gone even with 12ax7 in v1 and v2.I plan on moving input,tone and volume to the back side,damn it's going to be tight.

[Slimtim]

Thx a ton prr you nailed it.Moved vol,tone and power switch to the back and i f'ing love it.I don't mind the rear mounted controls just set and forget and use guitars.Plan on probably dropping a differnt tone stack in the future,amp seems real bass heavy at higher volumes.

[Slimtim]

And were back. 52 months later i finally just now updated that volume and tone.  .THx Doug for the patrs,worked like a charm.I went from the 18watt to the moonlight volume and tone.also removed the nfb loop and placed a zenith 12at7 made in germany in v1.Sounding pretty damn good to me.I have a pretty sweet speaker boxed up in the corner waiting for me to build a little combo.probably start on that next week.More to come.  

[mresistor]

I converted my AO-35 to a Carmen Ghia..    I mounted my tone/volume pots right under the OT and it had no ill effect.  very quiet. 

[Slimtim]

i used uncle doug's guide he did on youtube.except i removed nfb.it's a slow work in progress.but its getting there.