5f6a field trial

[lmolter]

I lent my dyi 5F6a to my brother-in-law for a week of testing, since he plays better than I do. For the design, I chose Weber 10A125's throughout, Mercury ToneClone throughout, and oil-filled coupling caps. The 5881's were biased for 35ma. with a plate voltage of about 480.

So after a week of playing hacker blues (because he's a hack) and a little country and folk, his initial response of 'Omigod it sounds awesome' uttered after 10 minutes of playing time morphed into 'The mid-range is awesome, but anything above the 10th fret on high B and E pops'. I think he is referring to a sharp attack with some compression. However, he does not usually play at high volume (for his family's sake), and I thought the compression was more pronouned at high volume. He also said that the bass was not full. All in all, it sounds great he says, but it sounds the best with his Gibson semi-hollow body with Humbuckers. He wasn't as pleased with the sound of his Strat, nor of his Ovation acoustic-electric (no comment there).

So here's the 64-dollar question: Given his assessment of the tone (and I forgot to mention that his hearing is not so good), does anyone think my build delivers what would be expected from a decent Bassman clone, or do I have some tweaks to do? My plan is to sell this amp at some time and I'd rather not hack up the fiberboard by ripping out caps and such.

Larry

[pdf64]

You need to have him demonstrate the problems he's refering to, in order to make a proper assessment. Something horrible might be happening which hasn't turned up on the test bench. Peter.

[lmolter]

I lent the amp to a real musician who plays various guitars and basses and his thoughts were that: 1) It's a great bass amp; 2) It's not a great guitar amp.

His reasons for not giving high marks as a guitar amp were just one: The highs were muddy. This goes along with my original post that a family member said the same thing, but I partially blamed it on the family member's loss of hearing.

That said, I speculate that my use of Vitamin-T oil-filled coupling caps instead of the ever-popular Orange Drops is the root cause. I searched the forums for threads about folks using those caps, but I found nothing. In fact, there is very little chatter anywhere about the Vitamin-T's.

So, for those folks who have built Bassman clones and are extremely satisfied with the tonal qualities, which caps do you recommend? And what do the Kendricks, Victorias, and other well-regarded amps have in them?

Of course, if I'm off the mark here, please point me back in the proper direction. All else said, the build is stock with carbon comps in the signal path, metal film plate resistors, and Tung-Sol 5881's. All iron is MM Tone Clone (not Axiom with adjusted voltages).

Thanks to all for your continued help and guidance.

Larry

[Satamax]

480 plate voltage seems high for a bassman no? Well, as for the mudying of notes, may be try some orange drops. But, there might be other isues. Are you absolutely sure that your circuit is 100% corect? How many times i've seen this, an amp working all right, but the circuit is not done properly. Maybe try a litle bypass cap on the treble pot.

HTH.

Max.

[lmolter]

Well, it's more like 470 (I didn't have my voltage charts near me when I posted this). It's high because the PT is not the lowered-B+ model. Still within 20% of the 432v listed on the schematic.

Anyway... other than the highs being not a crisp as my testers would like, the amp is clean to 10, and probably to 12, but I couldn't test with it twelved because we live too close to our neighbor and they have a new baby. The midrange is awesome and the bottom is smooth. And to me, a non-player, all 3 chords that I know sounded great, including a little blues-in-A pentatonic run at fret 5. But to my serious musician friend and his metal-playing son, they noticed a definite lack of crispness in anything high on the neck. Oh, and I forgot to mention that I have 4 Weber 10A125's in the box. From what I've read here and elsewhere, they are considered to be good speakers for this amp.

It sounds like changing the caps may or may not make a difference. I'd rather not make a mess of the board if I can help it because I don't plan on keeping this amp. I need the seed money to start a 5E3, which I think may have better appeal for the home guitarist. The Bassman is a brute.

I've already made a mod to the presence control by bypassing it with a 4.7K as recommended here. But you think I should put a few hundred puffs (picofarads) or more around the treble control? Isn't this more like a band-aid than a fix of whatever the problem (if there really is one) is? So if there is a circuit issue, what would it be? The signals are clean throughout, and no other circuit mods were made. I wired directly from the original schematic. Could it be the OT? Personally, I vote for the caps <g>.

Thanks for your input,
Larry

[Diablo]

Victoria uses their own specification of cap...looks like an orange drop to me, and that would be polypropylene metalized film.

Clark uses SoZo caps...and that would be mylar film and foil.

My 5F6A clone uses NOS Sprague black beauty caps...mylar film and foil, and it sounds just fine. Same speakers as yours, but running 462 volts on the plates. I have the Victoria presence circuit mod - 4.7K resistor in parallel with the presence pot (25K), and the pot is in series with a .1mfd cap to ground - the pot is wired as a variable resistor.


Perhaps you have a problem with the wiring somewhere, or a cap or resistor is off-value?

[lmolter]

The problem here is me trying to define what 'muddy' is. I think muddy is too dire a term. How about 'not crispy, screechingly bright'? The overall tone is quite pleasant, but not bright enough I guess. But I don't think that a vintage '59 amp with Astron (oil-filled?) caps would sound that bright, either. But I'm not an expert yet <g>. What I should really do is find a Victoria or vintage Bassman and have my guys run a comparison. I just don't know anyone that has one. My musician friend said he'll ask around and maybe the studio has something similar we can try.

I've seen that Weber now carries SoZo's, but from what I've read, they are used more in the Deluxe and Marshalls because of the need for smooth distortion. Would I be dirtying up the Bassman by putting the SoZo's in there? I'll wait for a few replies before I purchase anything. The amp is still out for more field trials.

It's never easy, is it? (But it's fun).

L

[Diablo]

I have no trouble making my amp sound bright, especially in the bright channel. With the bass, middle, treble, and presence set on 6.....there should be no doubt about brightness. Maybe just haul your amp over to a shop that has a Reissue Bassman to compare?

[tubeswell]

The difference could well be in the speakers you chose. (Don't recall reading what you had in there). Weber reportedly does nice sounding 10" alnico speakers for this type of amp. (I must order some for my next build)

[Diablo]

The difference could well be in the speakers you chose. (Don't recall reading what you had in there). Weber reportedly does nice sounding 10" alnico speakers for this type of amp. (I must order some for my next build)

I don't think so....because he's using the Weber 10a125 speakers, same as in my amp build, and I don't have his problem.

Differences noted:
capacitors - Vitamin-T vs Sprague Mylar film and foil
transformers - MM vs Weber PT + Heyboer OT
presence circuit - ? vs Victoria style
tubes - Tungsol 5881 vs Phillips 5881 + 12AY7, 12 AX7, 12AX7 NOS
builder - Imolter vs Diablo

[lmolter]

Diablo, are your Sprague's the Orange Drop or something else? I've already placed an order for ODs, so I might as well try them. On to the OT: There;s been some lively discussion about the merits of Heyboer's paper bobbin versus MM's plastic bobbin. Almost as lively as to which tubes sound best. I'll stick with the MM OT for now unless someone can 100% pinpoint this as the sole problem.

Confession: I did run the amp for a short while with the speaker shorted accidentally. I thought I just had low volume, but it was the OT coils vibrating and whining. No heat or smoke or anything else and I never cranked it up. Could I have somehow ruined the OT? I'm looking for a 'No' here because I don't have a bankroll handy to buy more transformers.

As far as the other tubes go, the preamps and PI are EH, not NOS. Can this difference really make a difference?

So... it seems the biggest difference is that yours works and mine works less.

L

[Diablo]

Diablo, are your Sprague's the Orange Drop or something else? I've already placed an order for ODs, so I might as well try them. On to the OT: There;s been some lively discussion about the merits of Heyboer's paper bobbin versus MM's plastic bobbin. Almost as lively as to which tubes sound best. I'll stick with the MM OT for now unless someone can 100% pinpoint this as the sole problem.

Confession: I did run the amp for a short while with the speaker shorted accidentally. I thought I just had low volume, but it was the OT coils vibrating and whining. No heat or smoke or anything else and I never cranked it up. Could I have somehow ruined the OT? I'm looking for a 'No' here because I don't have a bankroll handy to buy more transformers.

As far as the other tubes go, the preamps and PI are EH, not NOS. Can this difference really make a difference?

So... it seems the biggest difference is that yours works and mine works less.

L

My Sprague caps are old black beauties (mylar film and foil), not orange drops.
I really can't say if you damaged your OT, if you think you did, the Heyboer model I used is HY018343 - a multitap (2,4,8 ohms) - $68 from Weber. I can't say if my tube selection makes a difference.

[MWJB]

Changing caps will make a subtle difference, but I don't think that brand of caps is the silver bullet in your case.

With a GZ34, 460-480vdc might be typical for a tweed bassman, these voltages are not high, the schematic's voltages are not relevant (20% is far too high a tolerance to have on B+ voltage, 20% refers top component values).

Kendricks & Clarks have redesigned layouts to avoid the problems that plagued the original amps.

How did you wire you first stage filter caps, 2x100uf 350v, each bypassed by 220K 2W resistors? That's what the builders you refer to do.

I suspect the majority of your problems simply lie with the way things have been laid out, take some pics of the board, backs of the pots, filter caps,tube sockets & post them here.

[txstrat]

Changing caps will make a subtle difference, but I don't think that brand of caps is the silver bullet in your case.

With a GZ34, 460-480vdc might be typical for a tweed bassman, these voltages are not high,

Not to forget that higher voltages deliver more highs. So the voltages shouldn't be the reason for the lack of high end.
I wonder why the amp is clean up to 10. I imagine it starting to growl at the latest at 8 on the dial.
Did you check all the values (components and voltages) in the preamp and PI?
Seems like the pre stages won't deliver enough juice to drive the power tubes. That might result in sort of a muddy tone as well.

[Satamax]

Not to forget that higher voltages deliver more highs. So the voltages shouldn't be the reason for the lack of high end.
I wonder why the amp is clean up to 10. I imagine it starting to growl at the latest at 8 on the dial.
Did you check all the values (components and voltages) in the preamp and PI?
Seems like the pre stages won't deliver enough juice to drive the power tubes. That might result in sort of a muddy tone as well.

Huhuhuhuh!

High voltages don't necessarily mean lots of hight. It also dépends on how it's biassed. Cold get more highs iirc.

Best regards.

Max.