Filtering in Silverface Deluxe Reverb

[Doug]

I'm trying to get rid of sloppy bass response in my newly aquired '76 Deluxe reverb. I've changed a coupling cap between the pre-amp from .01 to BF spec .001, helped. Can I boost up the filter caps to get a more solid bass response? I've read the tube rectifiers don't like to see big filter caps, how big can I go? I tried 40uf in the first two caps, seemed to help a little, is this too big? Also I've reduced negative feedback from 820 ohm to 5.6k, I know this is counter productive but I love what it did to the top end, I'm sure I'll have to compromise somewhere. I also put BF specs in the phase inverter. Any suggestions?
Thanks
Doug

[MWJB]

You can go as high as 100uf, or 2x220uf/350v in series, bypassed by 220K resistors (1 per cap, Super Reverb style). Try 40uf at the screen supply.

Upgrade (doubt if that will be universally perceived as the right word) to 6L6/5881 & GZ34?

New speaker?

[Bruce / Mission Amps]

The DR uses a 5U4GB tube rectifier and the tube has a rated limit of 40uF.
Don't go too much above that. A 100uF pair in series is probably OK.
The 5U4GB is ON almost instantly and that huge power supply capacitance will look like a dead short for a second or two, causing stress to the rectifier tube and the PT.

A GZ34/5AR4 can work in these if you use a pair of 6L6s but don't idle them much over 15 watts each as the PT is only rated to 120ma.
A pair of JJ6V6s can handle quite a bit of voltage and you might be able to bias them at around 9-10 watts each with a GZ34/5AR4 rectifier, but only if the B+ is not too nigh.
Why?
The SF amps use a power tranny that can deliver +25vac more to the rectifier then the blackface PT (so it can use a 5U4GB) and the B+ rail will be very high if you do use a GZ34.

This amp uses a small OT and you'll never get gut wrenching bass out of it.
You can get a bigger Hammond OT in there at around 6500 ohms.
To lower some of the flabby bass response, black face the phase inverter, reduce the coupling cap driving the phase inverter to nothing more then .0022uF to .0047uF.
Reduce the coupling caps driving the power tubes to .022uF to .047uF.
Try taking some of the 25uF cathode bypass caps of the preamp tubes and use a 4.7uF cap instead.

[Doug]

I can change the rectifier?

I wondered if I could go with the gz37, less drop, less sag? I think 100uf would do it. 40uf to the screen? Is that the first cap (16uf) after the choke? Will 100uf's fit under that cover? Will the additional filtering tighten up the bass like I'm hoping? Also, seems like I'm out of headroom with volume at about 4, that's where the bottom gets really sloppy. I've ordered new tubes, since these were seriously underbiased when I recieved the amp and I don't know for how long. My first 6v6 amp, so I'm interested in keeping it that way for a while. The speaker is a celestion silver, not great. I've run it out to other speakers and had slightly better results, but the speaker's not the real problem.
Thanks
Doug

[Doug]

Thanks Bruce, it's really getting there

I changed the PPI .1 caps to .022s, good, and bypass caps to 10uf or 4.7s in the vibrato channel and reverb circuit, better. I'm still not sure about the filtering, originally they were all five 16uf 450v. I've replaced the first pair with 40uf caps parallel, so is that 80uf? Was your suggestion of two 100uf in series equal to 50uf? Am I double the 40uf limit? I've ordered 20ufs for the remaining three caps. How do each of these caps affect the signal? I've read (Aspen Pittman) you can use a 10uf at the final filter? I like the reduced feedback, are there any ballpark specs for feedback resistor. I've considered the soul control, but I'd rather just find a compromise and nail it down. What about replacement speakers? Thinking Eminence or Jensen, nothing too british, I've got a Marshall...
Thanks again
Doug

[MWJB]

Yes, you are double the 40uf "limit" but don't panic, you should be OK.
(Have you also noticed that your 6V6s are also running over their limit? But you still dare to switch the amp on...shock, horror?) :-)

Subbing the 16uf to 20uf won't really make a noticeable difference. Fit the 20's in the PI/preamp stages and leave it at that.

Subbing 40uf at the screen supply may well make a difference that you can hear.

You're pretty well at your limit for the feedback resistor, the amp could lose stability if you go higher.

You could try subbing the 22K PI tail resistor for 10K, for more gain?

[MWJB]

A GZ37 is pretty well a direct replacement for a 5U4. The rated voltage drop may not be quite so significant in an amp that isn't drawing max the current.

With the JJ6V6 or 6L6/5881 (either are typically rated for 500v on the plates) you will be able to use a GZ34 (least voltage drop of the tube rectifiers) or even a solid state rectifier. Do not try the tighter rectifiers with NOS 6V6s, bias the JJs to 20mA max.

The tighter rectifier and the subsequently higher B+ will improve headroom. The 5881/6L6 option will also further improve dynamic response, as Bruce says, don't go mad with the plate current, see how 30mA sounds. (It's only a "6V6 amp" if its got 6V6s in it, it could just as eaily be a 6L6 amp with slightly undersized trannies, especially if it gets where you are going?).

Back to the filter caps for a moment, your 2x40uf in parallel (I'm assuming that they're 500v rating) are OK, but ideally whatever value you settle on, you should rewire the main filters as 2 caps in series...this will sound better. Bypass each main filter cap with a 220K 2W resistor. Sprague 100uf will be a tight fit, great caps but you may want to spare yourself a headache and go for physically smaller ones?

Yes the screen supply cap is the first cap after the choke.

[Doug]

Thanks for the filter tip

Thanks again,
I was afraid to go too far with the filtering and swap rectifiers, but I might try that road, along with the 40uf on the screens. I guess I was trying to duplicate a blackfacing I'd done on a dual showman reverb, ss rectifier, removed almost all feedback. Really happy with that, just didn't need 100 watts thought it would just transfer into a small combo. I was using info from Pittman's "Tube Amps" on blackfacing, twins well covered, deluxe to a lesser degree.
Doug