First Post - Carmen Ghia Build

[mtbrider405]

Hello all, I have been a long time reader of TAG and love it. I have built a handful of amps and have a fairly substantial amount of electronics experience.

I am currently working on 3 AO-35 CG conversions for myself and a couple friends. I have ordered all the components for the Phoenix build and I am bound and determined to use the stock Hammond chassis. That is where my question comes in. Does anyone have a board layout that will fit in the limited space of that chassis? My only idea so far was to take the Phoenix layout and scale it down on the computer and I have done that, but it is going to be tight. So, any recommendations on fitting it all in there wound be awesome. Any concern in mounting the board directly over the top of the OT?


Thanks for the help!

[mtbrider405]

Also, can anyone explain why the tip of the speaker jack is connected to R18 and everything behind it?

[Structo]

Yes, that is the negative feedback loop.

[mtbrider405]

Thanks Structo, any advice or tips on shrinking the Phoenix layout? I bought turret board material to build new ones but should I just try to squeeze it all onto the existing board?

[M Fowler]

I posted about my AO-35 build and decided I like the Lite IIB better so built that circuit on the stripped original Hammond board and I wired the first preamp tube parallel for more gain.

Uses two 12ax7 and 2 EL84s and a 5Y3 rectifier.

https://tubeamparchive.com/viewtopic.ph ... sc&start=0

https://tubeamparchive.com/viewtopic.ph ... light=ao35

Mark

[mtbrider405]

Thanks Mark, I have read your post about 100 times haha. Looks great by the way! I think I want to stick to the CG first. Then maybe try others later.

Ill post pics and give updates as I progress.

[M Fowler]

The second link above is the regular Z Carmen Ghia build I did and one you are building.

Mark

[mtbrider405]

Well I completed the build.... But.

I get signal and it is plenty loud, but there is this extremely loud high pitch signal that is constant. I haven't left it on for more than 10 seconds or so after the tubes warm up because I am afraid of damaging something.

Can anyone help diagnose this high pitch tone? I mean, its bad.

I am thrilled that I got signal on the first try but then this high pitch sound showed up and stole my thunder.

The voltage at point A on the Phoenix schemo is about 350v. The input and speaker jack are NOT isolated from the chassis and I am using them as grounds for the board. Both center taps from the PT and the earth from the wall are grounded near the PT.


Thanks to any help!

-Jason

[topbrent]

Try swapping the output transformer leads at the power tubes.

[mtbrider405]

Thanks for the reply!

I will try that this evening. I just realized I put the conjunctive filter in backwards. Would that make a difference? Should I put it in the correct way before trying to swap the OT leads? By putting it in backwards I mean the 5w resistor is connected to pin 7 of V4 and the cap is going to pin 7 of V3.

Not that I am questioning you, but what would swapping the OT leads at the output tubes do?

Thanks!
Jason


Another note: The loud high pitch tone is not effected by the volume/tone pots.

[M Fowler]

Not that I am questioning you, but what would swapping the OT leads at the output tubes do?

This a common occurrence the high pitched squeal will come on if the two primary OT wires are reversed. That is why I keep those two wires longer until I have fired the amp up or just leave them a little longer permanently incase I have to swap them around.

Fix the conjunctive filter first and then if the squeal continues reverse the OT primary wires.

Mark

[mtbrider405]

Thanks Mark!

I will do exactly that this evening. Fix the CF first then if need be swap the OT leads.

I'll let you know how it goes.

-Jason

[mtbrider405]

Alright, I swapped the OT leads and fixed the conjunctive filter. Fired right up and boy is it loud!

I have a couple of questions.

1. Would adding a pot in place of the NFB 3.3M resistor allow me to change the voicing/characteristics of the amp?

2. Every few minutes a fairly loud bit of noise shows up. It lasts for about 20 or so seconds and while it's happening, if I turn the volume pot down, the noise goes down as well.

Any ideas on how to fix this? Would shielding the underside of the chassis help this?

Thanks,
Jason

[M Fowler]

The amp needs to burn in for awhile and you need to take voltage readings.

Noise could be lead dress, poor soldering, bad tubes, etc.

The amp will be quieter inside the cab as well or with bottom chassis plate.

One schematic is using 2m2 instead or you could run a trim pot.

Mark

[Tone Lover]

I ran into that problem on my first plexi build, reflow your solder joints mine ended up on some wires I soldered under the board, I found it just before i took it out to the firing range to shoot it full of holes. (LOL).

Bill

Ive also had tubes cause these wierd problems check them first.