Taming the Beast

[acheld]

I recently built a Hoffman 5F6A Bassman that needs . . . taming.

Channel 2 sounds fabulous, but only when my spouse is out of the house.  It is simply too loud.   I don't gig, don't need the power - my bad  for building this.  I do have good experience with Deluxe Reverbs -- figured I'd just have to turn the volume dial back just a bit.  Yeah, no, it did not work out that way.

Channel 1 I do not enjoy at all, but this is the channel with Rk=820R with Ck=220uF, and can easily be altered to taste.

One last complaint: wow is this thing heavy.  Too heavy for This Old Back . . .

I suppose I could try to limit the voltage of the circuit, bring the bias way down, replace the 5881's with 6V6's, and maybe try less efficient speakers, etc -- that would be one approach. My gut tells me it will always be too loud for my family (this assumption may or may not be correct).

But I'm thinking it might be best to downgrade the PT and OT to lighter specs, and move over to a 6V6 configuration.

I'd appreciate your thoughts.

If I were to get new iron, I'd like to go as light as reasonable.   I looked at the specs for Hammond 290 BX which supports 138mA, which seems right.  Are there other smaller power transformers I should be considering?

As for the OT, I'm thinking the Hammond 1750PA might be good.  8K CT, 18 watts.   Other OT's to consider?

Hoffman schematic/layout:  https://el34world.com/Hoffman/files/Hoffman_5F6A.pdf

[tubenit]

What voltage do you have on node A on the B+rail ?   OR on the 5881 plates? 


JJ 6V6's are rated up to 500v and you might consider replacing the 5881 with 6V6's?  IF you have around 430v on the plates, I'd try the JJ 6V6's. 


On V1-3, try a 1.5k and 5uf cathode cap.  You can try something like 1.5k/10uf on V1-8 with the cathodes NOT sharing a resistor and cap.


You could also install a PPIMV to lower the volume.  I'd probably try that before replacing the speaker.


You can try a 12AY7 or 5751 in V2  and try a 12AT7 in V3 LTPI.  All those may help in lowering volume and gain.


with respect, Tubenit

[dwinstonwood]

acheld, the Hoffman Plexi 6V6 I just built is - as you know - very much like a 5F6A with a Pre-PIMV:
https://el34world.com/Forum/index.php?topic=27701.0

I live in an urban townhouse, and I can push the amp into overdrive without it being too loud. It has three 12AX7's and two 6V6's and I used the Hammond 290AX. It has both 550V and 650V secondaries. I used the 550 windings with a SS diode rectifier, and I have about 380VDC on the 6V6 plates.

You could use the power amp and iron that I used to tame the volume (and maybe add the MV, too). Just a suggestion.

[labb]

Any 20 watt tube amp with a good speaker is going to rattle the walls in most houses if you crank it up.

[dude]

I had a 5F6A years ago, a reissue that l bought a Hoffman assembled board to replace the PCB. Great amp, but like you say has to be nailed to get that great tone, definitely not a living room amp.
All the changes you and others recommended are all fine and might help but then it’s not a 59 Bassman.
My advice would be to build another amp from the funds you get selling it or just keep it, l regretted selling many fine amps l had over the years. The 6v6 Plexi is much like the Bassman, after all Marshall copied Fender in that respect. The 6v6 Plexi is loud, loud as a Deluxe Reverb…, but with a PPIMV, you can get Bassman tones at a lower volume. But I find choking an amp never sounds like a natural wide open one. I have a Fender 67 Vibro Champ, with a ten” speaker and sometimes run a 6L6, just the right tone for a living room setting. I didn’t butcher the amp, made a new grill and speaker, have the original. I did replace the OT with a 10 watt SE old paper wound, sounds much better than the small 5 watt original.
Look more at the 6v6 Plexi, you’ll get the closest to your 5F6A tones at a much lower volume.
Cheers, al

[acheld]

What voltage do you have on node A on the B+rail ?   OR on the 5881 plates?

438VDC at the plates.  "A" is 439VDC, "B" is 437. 

Any 20 watt tube amp with a good speaker is going to rattle the walls

You can count on that! 

I currently run a DR and BJ simultaneously off of an ABY splitter.  The DR has wonderful tone even with the volume set at "3";  I am less pleased with the BJ, though it is not bad, just not as glorious as the DR.   I was hoping to replace the BJ. 

LOL, as soon as I received the PT & OT for the 5F6A, it was clear that this build was likely to be musclebound.  I really do know better, but sometimes you have to go with the "bigger is better" theme.    To be clear, when family is not present, the 5F6A sounds fabulous when turned up.  But that isn't what I need.   

the Hoffman Plexi 6V6 I just built is - as you know - very much like a 5F6A with a Pre-PIMV:

Yup, I followed your build, and was thinking of doing just that.  But I also like the Champ idea.  I'm going to mull this over.  Also the idea re: Hammond 290AX sounds good, I will look at the specs.  I don't recall which OT you used . . . 

On V1-3, try a 1.5k and 5uf cathode cap.

Yes, exactly, I have some 2uF caps, so was going to tack in a 1.5k and 2uF instead of the existing 220uF and 820R.   Channel 2 sounds fine; if it ain't broke . . .

[sluckey]

I have some 2uF caps, so was going to tack in a 1.5k and 2uF instead of the existing 220uF and 820R.   Channel 2 sounds fine; if it ain't broke . . .

Before you do that, jump the channels. Play with it a bit. You may just decide to keep that dark channel as is.

[vampwizzard]

I agree with Sluckey. Really great sound jumpered together and the difference in tones between the two make it a lot easier to dial in something you'll like.

Smaller version would be more akin to the Hoffman plexi as someone already said. Also look at attenuators.

Rob Robinette has a micro bassman.. honestly all of his micro amps may be more in line with your current state of playing.

[SILVERGUN]

To tame the beast: (and make it way less of a 5F6a - but not have to switch to 6V6 or change transformers)
-Make it so you can switch out 2 of the 3 speakers (if the power handling of 1 speaker is enough)
-Switch in or just clip in a power resistor across the remaining speakers terminals (put a cap across if you lose too many highs). Chose the resistor value to match impedance of speaker jack.
Stop and report back
And, if it's just too heavy, move to only one speaker permanently. Give me the 2 speakers you take out. 


-Put a 12AU7 in the PI and change the shared cathode resistor to 2.7K
Try it and then try:
-Disconnect NFB
Stop and report back


- Make a permanent 50% PPIMV by inserting a 220K series resistors after C11 and C12 (bypass with caps to retain highs)