Advice on Tweaks to 5F6a circuit

[jlatrace]

I have been playing my 5F6a for several months now and would like to try some tweaks to the circuit to hear how the tone might change with the goal to tighten up the bass. I wanted to get the seasoned 5f6a builders thoughts before I did so. I have found that small changes can make a significant difference in the tone of an amp. Here is what I am considering:

On v1, changing the cathode bypass cap from 250uf to 25uf similar to the narrow panel bandmaster.

Increase the preamp filter in the first stage from 8uf to 16uf or 20uf. I noticed on the reissue Fender really increased this filter (44uf), which may account for its reviews as being stiff and too punchy.

Are there any other things that one might suggest I try if my goal is to experiment but not completely change the amp from the basic 5f6a circuit?

[MWJB]

40uf at the screen supply node?

Are your main filters a BF style totem pole (2x100uf/350v in series, bypassed by 220K resistors)?

SS rectifier?

Cathode bypass cap at V2, pin 3 (.68 to 25uf)?

Tighter power tubes?

20uf preamp filter is quite common on repros.

[jlatrace]

My amp is original schematic spec except that I did BF the power supply rectifier (2x100uf/350v in series, bypassed by 220K resistors) and beefed up the screen resistors.

I have a tube rectifier & NOS 5881 power tubes.

I like the sound of the amp in certain rooms, it becomes muddy in the hall where I use it the most.

I had thought of the v2 cathode change after viewing the bandmaster and the 68 plexi schematics.

Do you have any order of recommended changes if the goal is to tighten the sound of the bassman but not stiffen it up to the point of a 1960's JTM45/JMP50?

Also I infer from your response that changing the v-1 cathode bypass cap to 25uf would not make much difference, is my inference correct?

[MWJB]

V1 cathode bypass - sorry didn't mean to infer that this wasn't a good idea, go ahead.

How about leaving the 250uf cap where it is, but sub the 820 ohm resistor at V1, 3 for 1500. Split the cathodes and use a new 2.7K resistor at V1, 8. Bypass this with a 15uf cap. I personally don't care for the 100pf bright cap on the Bright volume pot so I remove it, this tweak gives a chimey-er sound to the Bright channel (compared to Normal) especially if using all 12AX7 in the preamp. It still sounds Fendery and you still have a stock normal channel.

[jlatrace]

Thanks, I'll give this a shot this weekend.

I don't have a 15uf but do have 10uf, it shouldn't make much difference if I sub a 10uf for the 15uf should it?

[MWJB]

No, not really.

[jlatrace]

I split V1 cathode and played with the values until I settled on the following:

1.6K resistor bypassed by 250uf cap in bass channel
1.6k resistor bypassed by 4.7uf cap.

I tried the 10uf and it didn't make much of a difference.

It has tighter bass but still is loose and very tweed bassman. I jumper the two channels together and mix the two for great and varied tone.

Thanks for the help.