Fender Bassman 59 Reissue - Mods

[roberto]

A moneyless guy asked me to mod his 8 years old, never serviced, Bassman combo: warmer sound, more harmonics, etc...

This is the schematic of the amp:
http://ampwares.com/schematics/59_bassman_manual.pdf

This is what I'll do:

1. dpdt switch ON-ON between noval socket 2 and 3 to switch R16 and R17 between 100k (stock value) and 56k
2. dpdt ON-OFF-ON switch between noval socket 1 and 2 to switch tail resistor R21 (6k8-22k-22k) and bright cap on bright volume C4 (100p-nothing-220p)
3. 50k linear trimmer instead of 27k NFB resistor R27
4. 220k 2W resistors from 6L6GCs' screens to ground
5. retubing (the only non-cheap thing, but it's needed) and biasing

Do you guys have some other cheap suggestions?

[jelle]

Run. Seriously. This one takes money to do right.

[martin manning]

Jelle, I'm curious as to what "doing it right" would include? Replace a lot of components with better quality, higher-rated ones? Gut it and rebuild it more like the original?

[jelle]

Filter caps, speakers. Signal caps. I call that a rebuild.

[roberto]

Of course it will be costy to "do it right": better supply caps, resistors, coupling caps, etc.. But costs is what I want to avoid.

[jelle]

You could try a set of new tubes with a 12ay7 in v1...maybe that will make the guy happy? Easy to try.

[roberto]

Already in the list, point five.

[jelle]

Combined with Chinese gz34 and TAD short bottle 6L6gc. I did not see the 12ay7 in the list...

[LeftyStrat]

A moneyless guy...

"Unsigned musician" is much nicer.

And instead of "homeless," use "Guitarist without a girlfriend."

[old tube]

I have one of these built 1999. When I got it a year ago, it was stock, apart from a recent cap job and new Ruby 6l6GCs (yuk!). It's a nice amp stock but has more of a modern feel than I suppose I was looking for and TBH a bit piercing and harsh when driven. Not really what I was looking for ... a kinda saggy old tweed.

I'm a great believer in NOS tubes, so I decided that I'd go for 5881's along with a tube rectifier and perhaps 12AYs.

I'd also found reams of info on making mods to get the amp closer to the sound of the original.

Spoke to my amp tech who recommend as a start point, minimal changes to better accommodate the valve changes.

Following was done

R21 changed from 6k8 to 10k
C24 disconnected
Bias adjustment pot installed (Taken off at R41 which was removed).

I'll cut a long story short but ended up with the following tube complement

Rectifier: NOS Tung Sol 5UG4
Power tubes: NOS Tung Sol 5881 (running at 440V and 34ma bias)
V1: NOS GE JAN 6072A
V2: EH 6072A (was pretty good in V! also but the GE edged it)
V3: NOS GE 12AX7

The amp is definitely not as overly bright as it was before with harmonically rich cleans up to about 4 on the vol control. Cranked it is no longer harsh, nice creamy breakup with notes moving into harmonic feedback ... like a fender voiced JTM45 with KT66's! Great touch sensitivity too and nice sag from the rectifier.

Really is a great amp now, would love to change the speakers, probably to Webers, but that is a big investment and pretty happy with it as is.

My only concern is that I'm running those lovely old Tungsols at 10% over max rated voltage, but they seem happy enough.

[jelle]

A moneyless guy...

"Unsigned musician" is much nicer.

And instead of "homeless," use "Guitarist without a girlfriend."

What do you call a drummer?

[LeftyStrat]

A moneyless guy...

"Unsigned musician" is much nicer.

And instead of "homeless," use "Guitarist without a girlfriend."

What do you call a drummer?

A guy that hangs around with musicians.

[jelle]

Right!

[roberto]

Thank you all for the suggestions for the unsigned misanthrope musician.

Sorry, I forgot the bias mod already planned:
R41 substitued with a 10k in series with 50k lin pot.

Thanks for the 12ay7 suggestion, I planned a Sylvania 12ax7 I have around but I will try the 12ay7 too.

Basically you suggest to go directly as close to the old 5f6a scheme as possible.

[Dai H.]

cheap?

-make sure all contacts are clean, tight
-put in a bias control
-change any components that need replacing (filters, whatever)
-put in a tube rectifier, possibly one with a relatively higher voltage drop
-change tubes as necessary
-look at the pickup end (adjust resonance by varying C)