Need help deciding on the new Bassman build

[chikov]

Hello friends, I'm getting ready to start building an iconic Bassman amp but I need help deciding on what schematic to use. I want to use the one with a rectifiier tube and the long-tail pair phase inverter. Can anyone suggest a schematic with some modern modifications that improves the stability of the amp? This one I'd like to have a moderate amount of headroom... I just need to have some ideas to get the process rolling. May be there was a discussion on that topic already and I just missed it. I was spending much time working on guitars and got out of touch with the updates and upgrades in the Bassman fender world.
Thank you very mush,
Alex

[Stevem]

My pick would be the 5F6-A.
Stability comes from proper layout of the parts during construction.
3 things I would add during the build is (1) a hum balance pot for the filiments and (2) a bias adjustment set up such that if the adjustment pot goes open a resistor set up applies full bias voltage to the outputs so they do not burn up.

(3) is to add a 250 ohm 10 watt resistor across the speaker jack so the OT can never be damaged by an intermittent or fully open circuit.

A few build tips would be to use a star grounding layout.

Use shielded wire off of the input jacks to the first gain stages.

Lay the amp out such that grid wires are as short as possible and never run parallel with any plate wires .

Fight the common erg to put all the tone shaping components on a tag board, put them on the pots.
This change in a of itself will reduce the length of grid wire running in the amp which in turn will reduce the chance of oscillating and tone sucking effects.

Along these same lines the PI tube should be offset from the output tubes, but centered between them.

And the coupling caps off of the PI should go right on pin 5 of each output tube.
Once again this is all in a effort to keep high signal level grid wires as short as possible.

[martin manning]

I'm getting ready to start building an iconic Bassman amp but I need help deciding on what schematic to use. I want to use the one with a rectifier tube and the long-tail pair phase inverter.

Tweed 5F6-A 4x10 or Blonde 6G6 head?

[chikov]

My pick would be the 5F6-A.
Stability comes from proper layout of the parts during construction.
3 things I would add during the build is (1) a hum balance pot for the filiments and (2) a bias adjustment set up such that if the adjustment pot goes open a resistor set up applies full bias voltage to the outputs so they do not burn up.

(3) is to add a 250 ohm 10 watt resistor across the speaker jack so the OT can never be damaged by an intermittent or fully open circuit.

A few build tips would be to use a star grounding layout.

Use shielded wire off of the input jacks to the first gain stages.

Lay the amp out such that grid wires are as short as possible and never run parallel with any plate wires .

Fight the common erg to put all the tone shaping components on a tag board, put them on the pots.
This change in a of itself will reduce the length of grid wire running in the amp which in turn will reduce the chance of oscillating and tone sucking effects.

Along these same lines the PI tube should be offset from the output tubes, but centered between them.

And the coupling caps off of the PI should go right on pin 5 of each output tube.
Once again this is all in a effort to keep high signal level grid wires as short as possible.

I love all the suggestions! Thank you very much. I will definitely do all these mods and will base my schematic on 5F6. However, 5F6-A does not have the grid resistors (1.5k) on the output tubes - is it ok, or should I have them?

[chikov]

I'm getting ready to start building an iconic Bassman amp but I need help deciding on what schematic to use. I want to use the one with a rectifier tube and the long-tail pair phase inverter.

Tweed 5F6-A 4x10 or Blonde 6G6 head?

Both are excellent amps, but 6G6 uses diodes in the power supply circuit, but I'd like to use the tube for that (I have the transformer already).
However, your reply does help me to narrow my search for the "perfect' Bassman circuit.

[martin manning]

I'm getting ready to start building an iconic Bassman amp but I need help deciding on what schematic to use. I want to use the one with a rectifier tube and the long-tail pair phase inverter.

Tweed 5F6-A 4x10 or Blonde 6G6 head?

Both are excellent amps, but 6G6 uses diodes in the power supply circuit, but I'd like to use the tube for that (I have the transformer already).
However, your reply does help me to narrow my search for the "perfect' Bassman circuit.

6G6-A has solid state rectifiers. 6G6 uses 5AR4/GZ34.

[chikov]

I see... I will have to do some research and see which circuit will be "better" for me. I always looked for more overdrive, but this time I look for more head room...

[Colossal]

I built a 6G6B and it's a great amp. Currently running EL34s in it.

[Stevem]

Only add grid stoppers if you need them to stop oscillation, this is why build layout is so important.

If you find you need them then only add the amount of resistance you need to stop the issue.

[gldtp99]

I built myself a 5F6A based clone head several years ago

Except it has:

1) A PPIMV
2) A Raw control
3) Is only a single channel (and a single guitar input) with a 12ax7 in V1 --- both halves of V1 running in parallel, going to a dual ganged Vol pot, and mixed by resistors after the Vol pot

This head was "ok" when I could only run it at low volumes --- when I finally got it in a situation where I could crank up the output section (6L6GC x 2) it turned into a different beast ---- When run with lower preamp gain, than I used to run, and the output section cranked up it turns into a sweet sounding, loud, beautiful amp that has the tone I want for the old skool rock/punk/country music we're doing now

I also have a nice '79 JMP Marshall 2104 head (same as a 2204 but it was originally in a 2x12 combo) in the room (and it's a fine amp) but its tone is a little too "modern" for the music we're doing --- that 5F6A head is hard to beat

[chikov]

I was out of town and missed a reply or two, but i am back and I have a semi off topic question. I heard over the years that the best tube for V1 (12ax7) is Mullard or Telefunken brand. Would anyone suggest to me what you would prefer and where should I buy (find) one, preferably NOS? Just the usual places like Ebay and Reverb? or is there another place i do not know about? Something below $150, if possible... If you know another brand that is "magic", would you share what is it?
Thanks.
PS. I have heard about PPIMV and a RAW control, but completely forgot - I will do some research - thanks for the ideas.
'

[gldtp99]

This is "My Opinion Only":

I do use Old Production 12ax7's in some amps and I believe they can make a difference --- But not always, in every amp

In a Classic Hiwatt DR504 or DR103 (or good clones) a Blackburn Mullard ecc83 (12ax7) is a thing of beauty --- but not "magic" in every case

NOS 12ax7's can be very expensive --- sometimes the extra cost might not be worth the increase in performance, or there may be no increase in performance at all (or it's so slight to be almost the same)

I use "Used Old Stock" tubes because I have many, many of them on hand (mostly pulls)

In a Fender clone I would try many examples of Old Production preamp tubes in the amp, until I made my final choice

In a Fender clone I'd try:

a) RCA 12ax7a
b) various GE 12ax7's
c) different Sylvania 12ax7's
d) different Western European made Phillips ecc83's --- Amperex, Bugle Boy, Valvo, etc, etc
e) various Tungsram and RFT ecc83/12ax7 -- from Hungary and old East Germany
f) various Japanese 12ax7's --- sometimes you find winners there
g) and others --- I'd also try new JJ's and Electro-Harmonix and Tung Sol RI and Shuguang 12ax7's to make sure I'm not having "tunnel vision" on the old tubes --- sometimes new tubes can sound great, sometimes there is a great deal of difference and the Old Production tubes sound much better

I get to try the tube(s) in the amp --- checking for Sound Quality and Stability ---- For a V1 tube, Stability is probably most important ---- I can try out 100's of tubes if I want to

I'm not sending off for just one (Very Expensive) "NOS" preamp tube and hoping it is the "Holy Grail" when it finally gets to me

The Tube Store usually has a decent selection of NOS preamp tubes:

https://www.thetubestore.com/preamp-tub ... tube-types

[gldtp99]

Also Tube Depot:

https://www.tubedepot.com/t/tubes/preamp-tubes

[chikov]

Thank you for your words of advise. Over the years I heard many stories and opinions on the "magic" of vintage tubes, but your reply gives a reasonable, well balanced overview of that topic. I found that the old tubes are more robust built. The new tubes do not show as good of a readings on my tube tester, but my theory is that the filaments have a different resistance these days and I think they do not glow as hot as the old ones. May be because a lot of them use DC current now, but i am not sure about that. Regardless, I ordered 2 old, German made, Telefunkens - I will see I my customer will hear any difference.
thanks again for your words of wisdom.

[chikov]

I have another question... I am putting together the list of all the parts for this amp and I saw this strange capacitor between the plates (anodes) of the PI tube. I circled it on the photo. It says 47 something, and on another schematic it said .00001. What is it for? Do I really need it (cause other schematics do not have it at all)? If I do need it, what size cap should I use?
Thank you!