Here is my latest build/re-build

[Randall]

Sorry if this is redundant for some, and thank you for those that helped me think through this.

I just completed a AB763 Deluxe Reverb Re-issue upgrade that was a horror story. Ripped out the PCB guts to re-build it as a P-P project. The fiberboard turned out to be conductive when it absorbed moisture, causing me untold grief. Scratchy pots, bias hum, creaks and groans, and pops. Eventually I ripped that build out and replaced it with a G-10 turret board. I finished it today.

All issues are gone. It works great, it sounds great. Not one tweak necessary. Very sucky road to this conclusion, BUT it works. Never again will I trust a black fiberboard. Over and done.

Here is a shot of my work, if it will work. The amp is so quiet with both volumes cranked that you can't really even tell that it's on. Long live the glass turret board!

[Leo_Gnardo]

All issues are gone. It works great, it sounds great. Not one tweak necessary. The amp is so quiet with both volumes cranked that you can't really even tell that it's on. Long live the glass turret board!

It was a long row to hoe but you done it! She's a beaut Randall. Big copper bus bar is a nice feature.

[Chuck H]

I have a lot of posts so narrowing the relevant stuff would be impossible. But I think the old timers here know that I'm not a fan of black fiberboard. Maybe it's just coincidence but three out of four black board amps I've worked either started with conductive boards or ended up with conductive boards after extensive modding. I DON'T think moisture is the only culprit. I think some of the old boards have enough carbon in them that they can align molecules under HV conditions and become permanently conductive. I've seen the same thing happen on tube sockets with carbon traces as well as "tombstone" mounts on fluorescent light fixtures. Carbon can align itself when exposed to HV and form a high value resistor. Any unwanted conductivity can spell disaster in a power supply or high gain application. Guitar amps are both!!! As I've read here so long ago, I've come to believe that a guitar amp is a modulated power supply first and foremost. And the signal that is set up to modulate it is very low gain. Ergo, most guitar amps incorporate a high gain preamp. If my above observations are even a little true black fiberboard has NO place in guitar amp construction. Good on you for knowing to replace the board. It's not often obvious. I actually refuse to work with black fiberboard amps unless replacing the board is part of the schedule.

[Randall]

The kick in the pants here that when it was all said and done, when presented with the evidence, the vendor (who graciously refunded my money) admitted that while not a modern style of building amps, the material does absorb moisture and become conductive and cause problems, but they sell it to supply the market of vintage repro builders. Man, did that ever cure me of that blind affliction. Same with carbon comp resistors. Same with cab builders who want to charge $45 extra to move a 5E3 baffle 1/4" to accommodate a modern speaker like a celestion blue.

[silverfox]

I've come to believe that a guitar amp is a modulated power supply first and foremost.

Hi Chuck, as a newbie not too long ago, I had stated that exact hypothesis on a different forum and was abruptly corrected. You reconfirm my suspicions. While it may only be a method of analysis thinking in those terms, I too find it useful.

Silverfox.

[Leo_Gnardo]

Hi Chuck, as a newbie not too long ago, I had stated that exact hypothesis on a different forum and was abruptly corrected. You reconfirm my suspicions. While it may only be a method of analysis thinking in those terms, I too find it useful.

Silverfox.

Corrected. I'm sure you mean that in a pejorative sense. I knew you did...

Some of the best sounding hi fi amps I ever heard were some old Kepco "Programmable Power Supplies" rated 0 to 30 kHz, a friend liberated out of the dumpster behind the physics department at Stevens Tech in Hoboken NJ. Solid state too. Needed a BNC to RCA adapter cable for inputs to each one but so what, that's a small price to pay for a good amp.

I'm sure it's possible to get charming distortion out of amps with substandard power supplies - heck it's the basis of many an old guitar amp and their modern copies. But any way you slice it, you're right, an amp IS a modulated power supply.

[mort]

On this topic has anyone encountered problems with the grey vulcanized fiber board blanks like the ones they have at AES ?

[Leo_Gnardo]

On this topic has anyone encountered problems with the grey vulcanized fiber board blanks like the ones they have at AES ?

Haven't got any of these from AES, but I notice old late 60's - early 70's Traynors built on grey or tan fiber board don't have leakage problems. Nor 80's Fenders - the Rivera-designed amps - Concert, Princeton II, Deluxe II, etc all using grey board with eyelets. If you like doing eyelet-board builds, I'd take a chance on the item you pictured.

[Chuck H]

Agree. I don't think grey is the new black. It takes a lot of black to make something black and the amount of black is where the risk is.

On that note... I bought a 4x4 sheet of G-10 eight years ago for $80 and I'm STILL making boards off it. I estimate it's possible to cut 60 to 100 typical eyelet boards from a piece like that depending on the size.

[big_teee]

I've always used the natural Greenish colored G-10.
Always been skeptical of anything colored black.
I think Black, I think Carbon, I think Continuity!
T

[Chuck H]

And be careful what you mark your boards and components with! Pencil, for example, is highly conductive. A lot of guys use black Sharpie marker. I've never tested it. I just use purple or green!

[Alan0354]

I've come to believe that a guitar amp is a modulated power supply first and foremost. And the signal that is set up to modulate it is very low gain. Ergo, most guitar amps incorporate a high gain preamp.

Can you explain what do you mean?

Also, are the old BF and SF amp use black fiber board you think it's a problem?

[Chuck H]

Can you explain what do you mean?

An amplifier is taking the power from the wall and filtering it with your guitar signal before it gets to the speaker... Pretty much. There's more to it than that, but, seen in these terms it's easier for me to understand how changes to an amps power supply can affect tone and performance.

Also, are the old BF and SF amp use black fiber board you think it's a problem?

Yes. I've personally come across and heard of many more cases of conductive circuit boards in those amps. With so many having been made I guess you can still call the problem rare. But it's still a real problem that comes up sometimes.

[Alan0354]

An amplifier is taking the power from the wall and filtering it with your guitar signal before it gets to the speaker... Pretty much. There's more to it than that, but, seen in these terms it's easier for me to understand how changes to an amps power supply can affect tone and performance.

Are you referring to difference between regulated supply vs SS rectifier vs tube rectifier? Mainly about sag?

Or are you extending it to the size of the filter caps can change the sound?

[big_teee]

And be careful what you mark your boards and components with! Pencil, for example, is highly conductive. A lot of guys use black Sharpie marker. I've never tested it. I just use purple or green!

I agree.
When I drill and make a new board, I use a scribe, or scratch awl.
No pencil or pen marks.
T