59 Bassman LTD

[Hayden]

Hi
I have one of these and really enjoy it with single coil pup's but find it a little too "bassy" with HB's.
I have read a bit about the differences between the 59's tone stack values and the original values and I am considering making this change.
I was wondering if anyone here could tell me if there will be a huge tonal difference between using a 56k slope resistor, 47k resistor and say a 33k?
Thanks

[marcoloco961]

Hi
I have one of these and really enjoy it with single coil pup's but find it a little too "bassy" with HB's.
I have read a bit about the differences between the 59's tone stack values and the original values and I am considering making this change.
I was wondering if anyone here could tell me if there will be a huge tonal difference between using a 56k slope resistor, 47k resistor and say a 33k?
Thanks

You will "boost" the lower frequencies the lower you go with the slope resistor. If you are running the 100k slope right now and have too much bass then lowering it is probably not the answer. I don't think you would want to raise the value much above 100k either. Looks like the bass cap in your stack is a .1uF or 100n. A .022 or 22n is commonly used here in tone stacks, this will eliminate some of the really low frequencies. If that doesn't help you could lower the value of the coupling cap coming out of the first gain stage slightly. From a .022 to maybe a .01 or even a .0068 or so. Using a smaller coupling cap early in the circuit seems to make for "tighter" bass response.

[tictac]

Yes you don't want to change the slope resistor to get less bass....

The one component that can change the entire amp is the cap on the input to the P.I. If you've got a .02 in there things can get a bit woofy...

Try a .01 and then a .005 and see what you like best. I really like the feel of a .01; you still have decent bass response but with more control

With this modification you control everything coming from the preamp and it's easy to tweak or return to original...

TT

[Hayden]

Thanks for the quick answers - Just to clarify the bass cap is a .1uF and I am going to change that cap to 0.022uF as per "original".
I guess I was asking what the slope resistor at 100k to a 56k or lower change would do? (As the "original" value is 56k)

(Also the PI cap is 0.022uF which is the same as "original")

Thanks

[marcoloco961]

Thanks for the quick answers - Just to clarify the bass cap is a .1uF and I am going to change that cap to 0.022uF as per "original".
I guess I was asking what the slope resistor at 100k to a 56k or lower change would do? (As the "original" value is 56k)

(Also the PI cap is 0.022uF which is the same as "original")

Thanks

If the original slope resistor is a 56k then you might change it to a larger value to see if you like it. Any value between 56 and 100k might get you where you are looking to go.

[martin manning]

I think by "original" Hayden means the values shown on the old Fender 5F6-A schematic which is dated 1956 (100k slope, 0.2uF bass cap, 10k PI tail). Gut shots of actual examples (from '59 e.g.) show a 100k slope, 0.1uF bass cap, and a 6k8 tail resistor on the PI, which are the values used in the reissues. The 0.02 in place of the 0.1 bass cap will reduce the extreme bottom end, and the 56k vs 100k slope is a bit less of the mid-scoop (3-4 dB) moved up 150-200hz.

[Structo]

Looks like that amp is PCB, too bad.

Do you use the normal input?

V1a and V1b share a cathode resistor and cap.

The cap C1, is listed as a 220uF 25v which is going to bypass all frequencies.

You could experiment with that value.

Try a 25uF.

But being a PCB amp that will entail lifting the PCB.

[Jana]

Changing the 250uf cathode cap is a good idea but changing it to 25uf won't give an appreciable effect--the roll-off is still in way below the guitar frequencies. I would try a 1uf instead.

[tubeswell]

What Jana said