"Fiddy" 50-watt build log

[xtian]

See you got 4 more plates there - what's next ?

Added a badge to "Twenty," my Traynor YBA build, and am finishing up a small-box head cab for my Clubman build.

That leaves a few for future builds, which will not, NOT, I say, be happening until I sell a few of these finished ones. You know how it goes.

But I really do want to build another 18-watt.

[xtian]

So Fiddy V3 sat in the music store for four months. Lots of interest, but no sale yet. Staff said it had become their go-to demo amp, which is cool. But the power lamp broke, and there was bacon frying, so I brought it home.

Lamp was an easy fix (busted solder joint). Bacon frying turned out to be a leaky 500p silver mica cap, the one leading to the Treble pot. It was leaking DC like a freaking sieve. Anyone notice a high failure rate with silver micas from CEdist?

[Blackburn]

Haven't had any of mine fail yet, but I did just start using CDE micas instead. You can find them pretty cheap on Fleabay.

[deeder]

xtian,
Could you explain why you use 1.5K input grid resistor in place of the regular 5.6K soldered at pin 5?
Is it the right circuit design for a PPIMV? Thanks!

[xtian]

Could you explain why you use 1.5K input grid resistor in place of the regular 5.6K soldered at pin 5?

The original Marshall 1987 schematic has neither screen nor grid resistors on the power tubes. I added these for safety.

Where do you normally see 5K6 grid resistors?

Is it the right circuit design for a PPIMV? Thanks!

I'm not sure what you're asking. My PPIMV is very standard.

[cbass]

Looks good cant wait to see the lit up cab

[Colossal]

But I really do want to build another 18-watt.

Lite IIb type?

[deeder]

The original Marshall 1987 schematic has neither screen nor grid resistors on the power tubes. I added these for safety.?

Where do you normally see 5K6 grid resistors?.?

Actually I'm following this schematic found on Steve Miller site and think it is accurate to install a PPIMV into my 1987 build. As you can see it's a 5k6 grid resistor on the power socket (the same for 1959 or 2203): http://home.comcast.net/~jbjdav26/1987PPIMVr17.jpg

[xtian]

Guy in SoCal bought Fiddy V3, and just posted this video:

https://www.youtube.com/watch?v=I9L1DyzsfXk

Rock!

[lord preset]

Congrats. But how did you achieve that "recorded with a cheap cell phone" tone? Strategically placed CCs? Rare NOS cathode caps? I must know!

[xtian]

Oh, crap. I dug my 1983 Marshall JCM 800 2203 out of the closet, and it puts my Fiddy to shame in terms of tone. It's the proverbial wet blanket effect--the Fiddy is covered, the JCM simply shines. (FYI, I removed the JCM's bright cap and treble peaker. Oh, and it's got 31-year-old filter caps!)

So I'm considering swapping components in the Fiddy's tone stack. Check what I've got in there now: Mallory 150s, silver mica, carbon comp, old Astron in the presence control. Values are stock.

If this seems like a worthwhile pursuit, please suggest components to try. WIMA-style box caps like the JCM?

[JoeCon]

It's definitely the blue board. The "Fowler Effect" ...Look it up.....
Or the "Reverse Fowler Effect". One or the other.

[Colossal]

Dude, before you attack the components, what transformers do you have in the Fiddy? Old Drakes in the JCM

[drew]

Swap the tubes?

[xtian]

JCM has Drake trannies, JJ tubes.

Fiddy has Tweed Bassman PT, ClassicTone OT, Mullard (reissue Russian) EL34s, variety of preamp tubes.