Bassman Chassis 1959 - What is under the hood ?

[Raja_Kentut]

Hello folks,
I'm currently planning my next project. It's going to be a Bassman 5F6-A.
I have now discovered pictures where there is a metal cover on the top of the chassis. My question: What is under the hood?

Chassis Bassman 1959.jpg

viele Grüße,
Raja

[gonzomode]

B+ filter capacitors, I think it‘s called doghouse.

Gruß,
Josef

[bepone]

it is possible tu buy everywhere ie. tube town ..

[maxkracht]

You can also relocate some or all of those caps to the main board for an improved ground scheme if you are planning to build your own board, though probably a bit tight in a tweed style chassis. Larger chassis are more fun to build in, if the tweed-era chassis aesthetic isn't important to you.

[Raja_Kentut]

thank you all for the answers!
So no „hidden secret“ is there…

I‘ll build my own chassis, big enough to place all into it. (as one of my idols said: „Form follows function“).
I want the sound, not the appearance. If it's in keeping with the era, I'm happy to make compromises. For example, I almost only use point-to-point wiring, and I let my imagination run wild with the cabinets, but I stick roughly to the dimensions and colors of the time.

[martin manning]

You can also relocate some or all of those caps to the main board for an improved ground scheme if you are planning to build your own board, though probably a bit tight in a tweed style chassis.

Modern caps are much smaller than the 1959 originals, so it's relatively easy to put everything inside.

[maxkracht]

Modern caps are much smaller than the 1959 originals, so it's relatively easy to put everything inside.

Certainly doable, and possibly easy, depending on your skill level/dexterity. I do have some shockingly small 10uf 500v nichicons. Still a lot tighter than a BF/SF chassis, though I guess potentially more suitable for a point to point layout.

[Traynor]

Just a heads up, the 5F6A schematic is not the most common built Tweed Bassman. Do some research, the tone stack changed over the years.

[Raja_Kentut]

thanks Traynor, I will start with this circuit diagram. (see below)

IMG_0960.jpeg

If you have links to other versions, I would be grateful for them.
I meanwhile believe that there is no such thing as "the" tone, as can be seen from the fact that the voltages in the circuit diagram are specified as +-20%, and the PI resistors that are supposed to be particularly accurate still at 5%…
So the best (individual) solution will ultimately be found by trialling.
Nevertheless, I always want to stay close to the original...

I will build a head, at the moment there is a 20W class A amplifier in the cabinet with a transmitter tube from the old GDR

IMG_0962.jpeg

If my budget allows it again (man, the components have become expensive!) I will build a 4x10" loudspeaker box with the original dimensions I have got from this forum. The neighbors will be very pleased…

[martin manning]

The schematic you have is AFAIK the only one available for 5F6-A. Photos of vintage amps show that in production the tone stack used a 100k slope resistor (in place of 56k), and 100n bass cap (in place of 20n), and that the PI tail resistor was 6k8 (not 10k).

[Raja_Kentut]

thank you, I‘ll try that values. When I‘m done with this build, I‘ll post the sound samples of both versions…

[WhopperPlate]

Photos of vintage amps show that in production the tone stack used a 100k slope resistor (in place of 56k), and 100n bass cap (in place of 20n)

And some photos show the 20n and 56k values

I have quoted another post on a different forum .

“Fender used 3 different setups:

- 250pF, 0.02µF, 0.02µF

- 250pF, 0.02µF 0.1µF

-250pF, 0.05µF, 0.1µF
​
I've heard conflicting stories about which was "the most common setup" though all accounts seem to agree the 0.02µ/0.02µF was the least-common.”

[martin manning]

Another data point is the Fender reissue Bassman, which one could assume is the result of some study on their part.

[Raja_Kentut]

ok, thank you very much,
now I'll take bets on which one sounds best

[bepone]

it is cca 1min 30 sec if we count from cold iron to heat up to replacement of the component in the tone stack in the point to point circuit.
for all the options less than 10 min with sound test included

usually i go with 20nf + 20nF but i replace one of the cap for sozo to get some mojo