My 5F6A build vs. others

[tweed5259]

Forgive the basic nature of my question, but I have to ask, I'm completely out of ideas...

So I built a 5F6A clone from scratch, I used a Hoffman 5F6A board, cloth solid core wire, I have schematic correct voltages from the PT, a MM OT, MM Choke, Mallory Caps, Carbon Comp Resistors, and Weber Sig10s speakers, with Tung Sol 5881 power tubes, and JJ GZ34, and various preamp tubes to choose from. Pine Cab and Baffle board.

Now I've done the comparison to see how my built holds up against the clones and two original 1959 and 1958 Fender Bassmans, and mine doesn't cut it.
The Victoria 45410, the Kendrick 4210, the Clark Piedmont, and the two original Fenders all have that same sound, that compressed, smooth tweed Bassman sound, where the lows are bell like and the highs are smooth, and the break up is just fantastic...my build does not, what I'm looking for is some suggestions from other builders as what I'm missing. My amp is exact to the Fender schematic but it doesn't sound as good as any of the clones or originals. What can I do to improve this and make it sound like any of these other amps?

Please forgive the nature of what I'm asking, I realize it's hard to respond to, but any advice would be GREATLY appreciated.

[cminor9]

Sounds like you used good quality components. Must be heartbreaking to have spent all that time and money for not-so-good results. I think you'll get it right though.

What specifically does or doesn't it do? Does it hum or buzz? Is it not loud enough? Does it not break up like it should? If all of that is ok, but the tone isn't what it should be, have you tried different tubes? You sure you have the right value components throughout? Have you measured the voltages and checked them against the schematic? If all of the above, then do you have access to an oscilloscope? That might help you see the problem.

I see you are new here. I just finished my first build a while ago. If you can provide some specifics (any) then I'll bet you'll get the help you need here. This is a good forum. I had a few problems, and I have modded and tweaked my 5E3, messed it up, fixed it, and so on. This forum helped me along. Don't get discouraged.

[Bruce / Mission Amps]

Aren't those Sig10s the cheapest 10" speaker Weber sells?
I wonder if they are just not any good for this amp.
What is the idle current of the power tubes?
They need to be set up fairly hot to get a good full tweed sound.
Set it back up and get some voltage measurements and give us some kind of baseline.

[BackwardsBoB]

Would those be new tubes and speakers? Break-in?

[MWJB]

"I have schematic correct voltages from the PT" - What!?! If you have 432vdc at the power tube plates, you are 40v down on a typical 5F6a repro, like the Victoria or the Kendrick.

Please post plate, screen, & cathode (for the preamp tubes) voltages and plate current for the power tubes.

Any chance you could try and descroibe in what way it falls short tonally?

[yankeerob]

Hello Tweed5259,

I built a 5F6A out of the iron from a HRDv - it's not a direct comparison as I don't have a tube rectifier (no 5V tap on the PT) - I've used a 100Ω 25W ally clad wirewound (inductive) resistor to get some sag in the FWBR supply (at the suggestion of a good handful of people here and it works a treat) and it does the business for what it is - my first build was total crap - I reworked it death - ended up salvaging the front half of the turret board; sawed the power supply end off and made a whole new power supply board - the rebuild works a treat... I too had the vintage cloth covered solid core wire in the first build - ditched it all for 105° tri-rated 18 gauge stranded copper in the second and the amp immediately had more 'life' - I'm not saying this is your problem but if you've used wire that's limiting current in any way then you're not gonna get as much poke out of it as you might otherwise... I know the cloth covered stuff looks the part but who's gonna look inside yer amp to see what wire you've used? It's just a thought...

[MWJB]

22 or 20 guage solid core is unlikely to limit current in any part of your amp, other than the heaters & I wouldn't go larger than 20 guage stranded for the preamp heaters as you'll have difficulties stuffing the wire in pins 4&5 of the 12AX7 sockets (18 gauge solid core will be fine).

The only DC wires that carry a lot of current are the ones to and from the standby switch, even then your PT secondary rating is unlikely to be much over 200mA, so any wire rated at whole amps is fine.

[tweed5259]

Aren't those Sig10s the cheapest 10" speaker Weber sells?
I wonder if they are just not any good for this amp.
What is the idle current of the power tubes?
They need to be set up fairly hot to get a good full tweed sound.
Set it back up and get some voltage measurements and give us some kind of baseline.

Hey, yea they're the cheap ones, but I've also tried The Eminence Legend 1028K
Speakers, the Eminence Little Buddy's, and the Jensen P10Rs Reissues.
The Webers I used because I played a home build that sounded awesome with those in it. The Webers are about a week old.

Right now I've got 2 Tung Sol 5881 reissues, BUT I also have some NOS Phillips 6L6WXT's, and some JJ 6L6GCs.


Also, I will open it up now and record voltages and post back. Thank you all so much for your help!!!

[tweed5259]

I've got about 10 hours on both...but I've got several other Tubes and Speakers here with me that are broken in and none of them give up the goods.

[tweed5259]

"I have schematic correct voltages from the PT" - What!?! If you have 432vdc at the power tube plates, you are 40v down on a typical 5F6a repro, like the Victoria or the Kendrick.

Please post plate, screen, & cathode (for the preamp tubes) voltages and plate current for the power tubes.

Any chance you could try and describe in what way it falls short tonally?

Ok, so now that I've actually measured and recorded the information, I'm not even on with the schematic, here's the results...

V1: plate 225v / 218v cathode:1.6v screen:321v
V2: plate 81v / 93v cathode: .5v screen:150v
V3: plate 281v/ 255v cathode:43.5v screen:323v

Power Tubes: Plate: 459v
Bias is at: -46v

Tonally it sounds very middle of the road, the other amps I'm comparing all have a very smooth and chimey high end, a very loose spongy bottom end,
and a really great smooth overdrive. And all the other clones are VERY touch responsive, and what I mean by that, is that you play the note and it's almost like the amp plays the note a little too.

Where as mine sounds very "REISSUE" like. Meaning stiff, dull, the highs are not brittle, but they're not smooth like a Kendrick or a Real 5F6A. and the low end is just there. It's got no loose compression at all, and the weird thing, is if I put a NOS 5U4 rectifier in there, it doesn't do anything for the sag at all.
It's almost like it just dulls the sound more than it already is.

I know it's like me describing what I thing blue looks like, and I apologize and really appreciate any advice...

[pdf64]

What are the screen voltages you are refering to on V1,2,3? I was assuming the grid, but you've listed V3 as at 323V.
What's the B+ and 6L6 plate V with the 5U4 in?
Have you got a osilloscope? If you're using 12ax7s all thru there's a lot of gain available, there might be some ultrasonics going on.
As Bruce asked, what bias current have you got on the power tubes?
Peter

[MWJB]

"V1: plate 225v / 218v cathode:1.6v screen:321v" I assume you mean grid instead of screen, you shouldn't have hundreds of volts dc here.

"V2: plate 81v / 93v cathode: .5v screen:150v" V2 plate voltage at pin 6 should be mid-300s to 400vdc, cathode voltage (pin 8) should be more than twice what you have. Voltage on the grid (pin 7) in this case should be about the same as the cathode at pin 8. Only the cathode at pin 3 should have lo dc. Something is wired wrong

"V3: plate 281v/ 255v cathode:43.5v screen:323v" You should be seeing a few 10's of volts at the grids, not hundreds. Seems a big difference between plate voltages, I'd expect 10 or 12v difference at most. Check resistor values.

-46v at the 6L6 grids is not a measurement that means anything, it doesn't tell us how much current the tubes are drawing as different brands have massively different requirements. Install 1ohm 2W resistors between pin 8 of each power tube and ground, and read the voltage at pin 8 in mV DC.

[tweed5259]

i made a mistake that's the voltages coming in from the filter caps. so disreguard the "screen voltage" part of the preamp tubes.

the bias current is -422v

[MWJB]

Your bias current is not "- anything v", it is a specifing number of DC mV measured at pin 8 of the output tubes, accross a 1ohm resistor. You cannot set your bias current by negative DC voltage at pin 5 alone. I would suggest that with many tubes -46v won't be enough to idle the tubes at realistic plate dissipation. Do you have a bias adjust pot?

OK, voltages feeding the plate resistors sounds more ball park, but something is definitely up at V2, assuming that you have a 12AX7 in there. Voltage at the filter cap should be the same as for V1, as they are both fed from the same place.

Please read off voltages at V2 pins 1, 3, 6, 7, 8. Check that resistor grounded from pin 8 is really 100K (brn/blk/yel). Pin 1 & pin 7 are connected by a jumper, 100K resistor connects from pin 1 to pin 6, wire from pin 6 runs to preamp filter cap?

[pdf64]

As a side issue to your bias learning curve, if you've wired it up as per the original 59 schematic, there's a mistake compared to how they were actually done, re the presence control, see this thread
http://www.fenderforum.com/forum.htm...32877&offset=0
However, with the presence on full it would make no difference.
Peter