Help My Build Layout (5F6A)

[tweed5259]

In a previous post I'm trying to identify the differences between the tone of my 5F6A and some of the boutique Bassmans I've heard. Here's the basic History...

1.)5F6A Hoffman Layout with 47pf cap on PI tube as per Fender Schematic
and 56K resistor on the phase inverter as per Ted Weber's Schematic.
2.)Presence Pot Wired to actual 5F6A pot from an original (with .1 cap and 4.7K resistor.)
3.)Mercury Magnetics Tone Clone OT and Choke (Fender PT - Voltages at 443v on the plates of the Reissue Tung Sol 5881's Biased at 34mA.)
4.)Weber Sig10s Alnico Speakers

HERE'S THE LAYOUT, http://s332.photobucket.com/albums/m336/tweed5259/

I'm asking to find the reasons that I feel My Build is not as Good Sounding as most of the clones I've played, or the Originals.

Thanks in Advance everyone, and I'll take any criticisms, maybe we can all learn from my mistakes in layout, I'll keep a detailed record here of the changes.

[MWJB]

OK, first things first...

As Bruce touched on previously, the amps you mention don't use Sig 10s...maybe just try some different speakers to eliminate them from enquiries...but realistically, you have 4 speakers & changing them is going to be expensive, you say you hve heard them sound great in another amp, so there are much cheaper avenues to explore first...

That 56K NFB resistor should be 27K. 56K will make the amp more aggressive.

That presence pot is 25K isn't it?

Those 1.5K grid stoppers on the power tubes should be shortened down, the resistor can but up against the socket pins, especially pin 5. 0.5W, carbon comps will do fine here.

None of the amps you mentioned in the previous thread used metal film/oxide plate resistors in the preamp, some use 0.5W allen bradley carbon comp types, you could try 1W carbon comp or carbon film.

I'm a bit confused by your filtering arrangement...there's only 1x22uf cap on the board, is that the preamp filter or is it the PI filter? Have you used 2x350v caps in series, bypassed with 220K smoothing resistors (like BF amp), for the main B+ filtering?

I don't want to sound brutal but no-one is going to mistake the wiring for Clark, Victoria or Kendrick :-). It might be parallax, but check the hot OT secondary wire at the RCA jacks look to be very close proximity to the grounded screws holding the jacks in place?

Grid wires should be short as possible, plate wires can be longer and away from grid wires, not running close & parallel.

go to Hoffmanamps.com then to library of info, hoffman board information, under "What is a hoffman board you'll see Doug's photo of an installed Plexi board, that's kind of what you are aiming for...won't be exactly the same because of the differing chassis dimensions but you'll get the idea...wires to pots could be a lot neater, less tangled, ideally your board could have been installed a little farther to the left to allow a straighter, shorter run of grid wires to PI & power tubes.

There is a degree of neatness required when wiring an amp, you're not quite there yet.

[Tubenit]

difference?

It would be helpful to know what the difference is that you're hearing?

I'm asking to find the reasons that I feel My Build is not as Good Sounding as most of the clones I've played, or the Originals.

The original and good sounding clones are more ______
and your amp is __________?

Speakers obviously make a BIG difference. Having hearing some great sounding messy PTP builds ........ I am less convinced that layout is always the culprit (although for higher gain amps it can be severly problematic).

With respect, Tubenit

[tweed5259]

Tubenit:
"The original and good sounding clones are more ______
and your amp is __________?"

the original and good sounding clones are more "chimey, smoother, no piercing highs, more acoustic like."

and my amp is harsher on the high end, and more "barking" when turned up.

MWJB:

What Speakers sound like 40 year old Jensens? The Italian Jenses sound gross.
The Weber Sig10s just don't give up the goods, they're better than the Jensens, but they're just warm, no sparkle in the highs and the bass is very boomy.

"The Presence pot is a 25K"

"metal film/oxide plate resistors" - these aren't in the signal path, you think this will matter?

The Filter Caps are in the can, theres 2 20uf tied together, then the one 8uf/600v, then that's stage 4 on the board there, it's a 20uf/500v cap. It just didn't fit in the can so I put it on the board.

I will be adjusting the layout, but I'm still missing something, If I had to describe it, it would be that mine sounds like it needs more smooth high end and even frequency response between highs, mids, and lows.

[tubeswell]

Yep speakers definitely make a huge diff to the sound.

Hey tweed5259 - If like myself you are homebuilding for your own edification (and not for any dreams about commercial enterprise), you can fossick around in junk shops and local tech shops for old treasures. I have had some successes and failures doing that. You might end up with a cluster of different types and brands (which can only add to the uniqueness right?). You would be more likely to find 12" speakers if you do that because are more common, so you might want to consider going to a 2 x 12 baffle (even as an experiment?)

12" Celestion Blues really can't be beat in terms of new products (and I have heard good reports about 30W Eminence Red Fangs). Otherwise if you want to stick with 10s, try some different specs of the products from Weber. (e.g.; go for speakers without the dope etc)

How broken-in are the speakers you have in there? They might need some more wearing in to develop the sound?

I would consider circuit mods (starting with coupling caps and cathode resistor/bypass cap type mods) after I had exhausted the speaker search. In terms of mojo there's all kinds of bumpf about different types of resistors and caps - you could be experimenting for a while... However if I can say this without needing to duck ;-) , I definitely find to my own ear that silver mica caps sound better than disc ceramics or polystyrene caps for treble caps in tone control circuits. I find disc ceramics to be quite bright (maybe that's what your'e looking for?), and polystryene caps not quite edgy enough, whereas I like the velvetyness of mica caps.

[MWJB]

"and my amp is harsher on the high end, and more "barking" when turned up." - that 56K NFB resistor won't be helping here.

"What Speakers sound like 40 year old Jensens? The Italian Jenses sound gross.
The Weber Sig10s just don't give up the goods, they're better than the Jensens, but they're just warm, no sparkle in the highs and the bass is very boomy." Good question, I'm sure that every manufacturer that has a P10R type speaker has the answer...unfortunately I don't (an original P10R reconed with the original KSP3 cone paper would have to be a candidate). Victoria use the Jensens don't they? Clark has options, Kendrick use their 10" ceramic blackframe.

"metal film/oxide plate resistors - these aren't in the signal path, you think this will matter?" - I've honestly never used metal film/oxide plate resistors, I have only ever played through one amp that did (I didn't like the amp but can't say that the plate resistors were why), it's really not very common for guitar amps to use anything other than carbon comp or carbon film - sub them out and see if you hear anything?

"The Filter Caps are in the can, theres 2 20uf tied together, then the one 8uf/600v, then that's stage 4 on the board there, it's a 20uf/500v cap. It just didn't fit in the can so I put it on the board." Lose the 2x20uf tied together and replace with 2x100uf in series, bypassed with 220K resistors (as per BF style). Lose the 8uf cap altogether, 20-40uf 500v will do at the screen supply, 20uf 500v each at the PI & preamp. Looking at your description you see to be a filter cap missing? The 2 tied together are presumably 40uf for the main B+, then you only mention 2 others, there should be 3 (at least) other caps?

Tubeswell said "I would consider circuit mods (starting with coupling caps and cathode resistor/bypass cap type mods) after I had exhausted the speaker search" Well, I'd avoid cathode resistor & bypass cap mods, we're not trying to alter the MO of the amp, at this stage, we're just trying to get it to a datum line, it would make more sense to get the amp 100% working with authentic values first. Speakers are typically the most expensive components in a 4x10" amp...it makes practical sense to see how far you can get before they become a limiting factor.

Tubenit wrote: "........ I am less convinced that layout is always the culprit (although for higher gain amps it can be severly problematic). " I'm assuming that you've looked at the photos, have you ever honestly seen a production amp that looked like that? We need to eliminate all possible causes of bad tone before redesigning the wheel in this case. You would be amazed at the difference moving or shortening the odd wire can sometimes make.

[tweed5259]

I'm gonna start with redoing the layout,

I have some Eminence Legend 1028K's (which are jensen clones)
I also have 2 reissue Jensen P10Rs, the Italian ones.
I have 2 Lil' Buddy Eminence 10's
and 4 Weber Sig10s

I'm gonna fool with all these in different combonations as well as fix the layout
and then I'll post back to see what's what. I'm also going to address the carbon comp/metal oxide resistor issues and see which I like better.

I'll post back when all this is done, should be a minute though.

thanks.

[MWJB]

The Emi 102s don't really sound like Jensens, they're darker, less fidelity.

[tweed5259]

Ok, Awesome, so now in my trying to redo the layout, I've got some sweet parasitics. And when I say parasitic, I mean the amp is possesed by a devil.
I sounds like a blown speaker on the low "E" then all of a sudden, it goes into full on shut down, all the voltages check out OK, but it sounds like it's eating itself.
I'm obviously a player, not a builder. oh but before it went crazy, I finally got one of those paper wound Heyboer OT's. sounded AMAZING for ten minutes.

crap.

[MWJB]

Post a pic of the latest layout.

[tweed5259]

wow wee, ok rewired and working fine.

whew.


sounds awesome now, actually way better than the Victoria i just tried out when I thought I had to replace mine. Mine has much more touch response and the highs on mine are rounder and more chimey not piercing at all.

I'm gonna make a post of what I've learned to hopefully save somebody some time and money.

[MWJB]

Good news, well done.

[nokaster]

i'm looking forward to your findings!

did you end up using the weber speakers?