"Fiddy" 50-watt build log

[Colossal]

JCM has Drake trannies, JJ tubes.

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

How do your B+1, 2, 3, voltages in the Fiddy compare to the JCM? Also, is the ClassicTone OT a Plexi clone, not a Bassman, like the PT?

[xtian]

Sorry, not ClassicTone. It's this:
https://www.tubesandmore.com/products/P-TM050

Fiddy has 490v on the plates. I don't have a record for the JCM's voltage.

[Reeltarded]

Less! Way.

Oh. 2203. Lots less, but not way less.

[xtian]

OK, I popped open the JCM. My mind is blown. I had 15mA current thru each power tube. 70% is closer to 35mA! How could it sound so good?

Scratching my head, but turned the bias up to about 30mA, voltage dropped to 450.

Pulling the Fiddy next. == As reported, 490 on plates, biased at 70%.

[xtian]

It's always helpful when you can A/B something to hear the difference!

Strat -> A/B/Y -> JCM and Fiddy -> 2x12 cab with stereo wiring, so JCM is in one speaker and Fiddy in the other Celestion G12K-85s and I can switch back and forth with the A/B/Y. During the experiment I swapped speakers also to make sure the speakers didn't sound different from each other.

First, I found I could get the tone stack on the Fiddy sounding a lot closer to the JCM (and my ideal) by tweaking. This made me happy. I got some great sounds out of her, while learning that most tone knobs need to be in the 1-3 o'clock range.

At all settings (clean, edge, hi-gain), it became apparent that the Fiddy's has an unwanted mid hump (around 1K, maybe?). The Mid control is not very effective. It's this hump that's making the Fiddy sound congested compared to the JCM.

Also, the Fiddy's Presence control acts very differently than the JCM. It rolls off more highs (a larger band) and more overall volume when reduced, and the highs it adds when increased are also wider band, and harsher, than the JCM.

So what do you guys think? Attack the tone controls (especially that Astron presence cap)? Or do you still think it's a combination of high voltage, tubes, other stuff?

[stevlech]

Just a thought: Is the Treble pot Linear or Audio taper?

[xtian]

Just a thought: Is the Treble pot Linear or Audio taper?

I don't remember; the pots are all reclaimed from a Tweed Bassman reissue.

[xtian]

GREAT NEWS.

I pulled the old Astron 0.1uF presence cap and the two Mallory 150 series 0.022uF tone stack caps, and replaced them with Vishay polypropylene box caps (http://www.vishay.com/docs/28119/mkp3382.pdf). I ordered the ones with long leads, so they're as easy as axial caps to work with.

The unpleasant nasal quality is GONE from the Fiddy. It sounds so much better. In A/B with the JCM, I can get it to sound much, much closer. Of course the JCM tears the Fiddy's head off in the loud and clean department. But the tone stack in the Fiddy is now sounding much more like my ideal.

[matt h]

(deleted)

[ampmike]

Lookin good my friend

[xtian]

Thanks for the props, guys. Yup, after tone stack surgery and with the addition of the FX loop, this amp is really floating my flotilla. Going to take it up the hill to play with a new group of talented gentlemen. Look at this ruh-donk, meathead set list:

If You Want Blood
Riff Raff
Ain't Talking Bout Love
Sweet Child of Mine
Hot for Teacher
Mississippi Queen
Heavy Metal

Fun.

[M Fowler]

Nice job on your amp.

I had to google flotilla: https://www.google.com/search?q=flotill ... 3&ie=UTF-8

[Smokebreak]

GREAT NEWS.

I pulled the old Astron 0.1uF presence cap and the two Mallory 150 series 0.022uF tone stack caps, and replaced them with Vishay polypropylene box caps (http://www.vishay.com/docs/28119/mkp3382.pdf). I ordered the ones with long leads, so they're as easy as axial caps to work with.

The unpleasant nasal quality is GONE from the Fiddy. It sounds so much better. In A/B with the JCM, I can get it to sound much, much closer. Of course the JCM tears the Fiddy's head off in the loud and clean department. But the tone stack in the Fiddy is now sounding much more like my ideal.

Hey man, I've used these caps before in marshalls and I really like them too!
However, I can't find them anywhere, and have no idea where I got my first batch from. I thought it was newark, but now I am crosseyed trying to find these damn things, and only slightly obsessed. Do you remember where you got them? I can only find the blue ones, or the grey shorties. I imagine any metalized polyprop will do, but nooooo...I have to have these

[xtian]

Here is the WIMA cap I used.

The mfgr part number is BFC233824104. The "24" indicates long leads, and the "104" at the end is the value.

EDIT: Woah! Really cheap at Newark. I find myself ordering there more and more often.

[Smokebreak]

Thanks man! I guess the color and lead lengths were was throwin me off. I'll put the 22n right here, for the next time I forget http://www.newark.com/vishay-bc-compone ... C233824223
http://www.mouser.com/ProductDetail/Vis ... GMQQ%3d%3d