apartment amp with a blackface sound

[tubescent]

i want to build an apartment amplifier. problem is i've become addicted to that blackface sound as have had opportunity to play a vibroverb, deluxe reverb and a twin recently and loved 'em. if i build a single ended blackface champ or maybe a dual single ended 2+6v6 amp will it still have the blackface vibe? or is the push-pull element of the design crucial to the sound of the bigger blackface amps?
basically in an ideal world i would love a vibroverb cut in half - with half the watts and just one of the 10" speakers but with 9/10 of the sound for apartment volume levels.
am i dreaming?

[txstrat]

I'd say you can come close to the black face sound with a single ended amp. Close, because there is not ONE black face sound. Even different BF amps sound different, depending on the speakers, cabs etc.
I think a Champ would work fine ( http://www.schematicheaven.com/fende...a764_schem.pdf ). The first tube of the Vibroverb sits in almost the same circuit as in the Champ (different mid resistor). Different power stage, as a matter of course. Have a look for the right speaker (I'd go for a 10'' Weber or Jensen but that's just MHO) and be aware, 5W are still half as loud as 50W.

[MWJB]

Well, there is no clear, one size fits all answer on this but a SE amp will typically have more crunchy, fuzzy harmonics compared to a PP amp (with as many of the other factors possible, being equal). There are obviously tricks to make such an amp sound smoother and more like a PP amp, but if the bigger PP amp tone is what you are after, PP is probably what you should stick with. Perhaps a BF preamp & PI mated to a single 12AU7/12BH7/6SN7 output section? All of these tubes are twin triodes, effectively 2 tubes in one and are suitable for low power PP.

For the 6SN7 a primary Z of around 8K will work, perhaps a plate voltage in the early 300v range.

The final result will probably put out about as much power as a champ (5-7W...hope you have a big apartment).

[tubescent]

i realise blackfaces are an era of amps and different from each other but it's a ballpark sound i'm chasing.
after looking at a lot of blackface schems it looks to me that the sound (vs the tweed) comes down to
main elements:
- no cap on the preamp bias of v1
- tone stack with at least treble and bass
- bigger filters in the power supply
- choke
- negative feedback

other bits
- ceramic speakers
- fixed bias.

if i built a super champ (2+6v65, solid state rect, for about 8watts) but with the main blackface elements above would it be 90% of the blackface sound that i'm after? or is the push-pull hum cancelation and efficiency still part of the sound?
this is kind of really hard to compare in real life cause all the champs i've tried were tweed clones and smaller amps in general all seem to be shooting for at least a vox cranked sound or rockier. also most people who do champ builds go for the tweed.
or should i just tame a princeton reverb for home use using 6k6 tubes? heard this might be go. 6k6s are kind of a bit rare on this side of pond though.
if i go single ended build i figure using solid state rect and a choke is not much of a tradeoff cause i keep hearing that single ended designs don't sag anyway. i just don't want to spend time on a single ended build cause of volume issues and then end up with a sound that is too raw for what i'm wanting - which is kind of every champ i've ever tried or heard. i love 'em don't get me wrong but that's not what i'm chasin at mo.

[Steve Conner]

I can't crank a 5 watt amp in my apartment without my neighbours complaining.

The AX84 Firefly shows how to make a tiny low-power PP output stage.

Or you could build yourself a full-size Vibroverb and add an attenuator to the output. Same idea as a trumpet player, the attenuator "puts a sock in it" so you can practice at home, but when you take the thing out to a gig, you can let the full power rip.

A good attenuator also lets you adjust the amount of "sock", so you can attenuate it a little and get lots of clean headroom, or conversely, crank the amp volume and soak away 99% of the resulting power.

[tubescent]

hehe don't have a big apartment but i work nights so can play during days. anyway i don't want to totally dime the amp i just want it working so that it's on about half the dial but i'm not goin deaf.
i might try those different tubes - need to change bias resistors? is there any more to it than that or are they pretty interchangable into 12ax7 designs?

[txstrat]

90% of the blackface sound that i'm after? or is the push-pull hum cancelation and efficiency still part of the sound?

At what volume did you play those mentioned amps?
A push pull amp played at volume on 2 (wich could still be too much for the most apartments) would never sound like the same amp on stage at volume on 4 or 6, with the right amount of power amp saturation.
The single ended amp at 6 would add too much grit to the sound here, right.
But if you play it on bed room level (or maybe living room level) the difference is not that big. Maybe a Princeton reverb?

[MWJB]

All Fenders have a cathode bypass cap at V1, the fact that it is omitted on the 5F1 schem is a mistake.

tone stack with at least treble and bass - and that tone stack being plate fed, from the input stage, feeding the vol control - not fed by a cathode follower after a volume control. Also the ability to scoop the mids for a BF...which even a 5F2A can do well enough.

positioning the choke between B+ & screens (as opposed to after the rectifier & before B+ on 5E# tweeds), running high screen voltages.

NFB - not an issue, equally as prevalent on big push pull tweeds after '56.

Filtration - moot point, 20uf preamp filter on a bassman doesn't make it a BF.

Some BF/SFs had alnico speakers. Ceramics in a tweed don't transform it to a BF.

Don't get hung up on the fixed bias, champs were never fixed bias (though they can be). If you go low power, cathode bias is still an option.

"if i go single ended build i figure using solid state rect and a choke is not much of a tradeoff cause i keep hearing that single ended designs don't sag anyway.! A lie repeated becomes the truth - re read Aikens article, then re read it again...this is often misquoted, it applies to a class A amp, running class A, within it's power rating - not really to a champ, which is typically a budget SE amp, run hard, that happens to fall into broad class A spec by accident.

A factor worth noting is relatively high preamp plate voltages, >220v.

"which is kind of every champ i've ever tried or heard. i love 'em don't get me wrong but that's not what i'm chasin at mo." then don't build a champ.

Even 2x 6K6 in PP don't really equate to an apartment amp.

[txstrat]

The main thing is that a BF amp sounds at it's best, when the power tubes are driven to some degree. That (understandable) is just too loud for appartment use, if you live alone or not. Unless you're trying to get yourself deaf.
I've built a Champ II copy (I only added a 25K mid pot) which has a BF sort of preamp (one more triode) and a master volume. You can dial in the right amount of grit with the preamp and adjust the overall volume with the master.
This thing can go from BF clean to almost Boogie like dirt.

[MWJB]

"i might try those different tubes - need to change bias resistors? is there any more to it than that or are they pretty interchangable into 12ax7 designs?" - please clarify?..if you mean the 12AU/BH/6SN7, then I meant for these to be in place of an existing output section (you'd have to build it), not as tube subs for an existing BF amp. I don't recommend a 12AX7 output section.

Some of your perceptions seem to be more based on drawings & schematics, rather than the sounds that amps make...here's an idea, why not try buying an SF champ, trying some mods (mid pot, fixed bias, bigger output tube, SS rectifier, bigger OT, 10" speaker) use it as learning process....then maybe try building a low power PP amp.

[tubescent]

oops sorry got mixed up for a minute and thought you were talking about v2 PI - apologies still a newbie

[tubescent]

"i might try those different tubes - need to change bias resistors? is there any more to it than that or are they pretty interchangable into 12ax7 designs?" - please clarify?..if you mean the 12AU/BH/6SN7, then I meant for these to be in place of an existing output section (you'd have to build it), not as tube subs for an existing BF amp. I don't recommend a 12AX7 output section.

Some of your perceptions seem to be more based on drawings & schematics, rather than the sounds that amps make...here's an idea, why not try buying an SF champ, trying some mods (mid pot, fixed bias, bigger output tube, SS rectifier, bigger OT, 10" speaker) use it as learning process....then maybe try building a low power PP amp.

i have been trying a lot of amps but also looking at a lot of schematics exactly because i'm trying to learn about how different parts of tube amps affect the end sound result. i think your idea of the SF champ is a great cheap platform to try some stuff (i won't do anything unreversable) and then sell it on if i go PP.
just for my knowledge and interest - could you steer me towards a schem or info on a low power PP amp? did a google search and came up with nothin. only low power PP amp i ever came across was for audio application.

[yunger]

it just so happens i am working on a bedroom-blackface for a friend. here's the circuit i came up with for my amp. take from it what you will.

[MWJB]

"just for my knowledge and interest - could you steer me towards a schem or info on a low power PP amp? did a google search and came up with nothin. only low power PP amp i ever came across was for audio application." Steve O'Connor has already referenced the AX84 site, there are some self split push pul designs there (Firefly?), copy these from the poweer tubes to the OT. Copy preamp & PI tube from say a Deluxe, then the PI feeds each half of a 6SN7 (instead of feeding both 6V6s), the plates of the twin triode tube then feed each end of a small PP OT, 8K primary impedance, say 30-40mA rating (Hammond 125A/B?). You don't need to worry about the screen connections (pin 4 of the 6V6, 470ohm resistors) or a choke as the 6SN7 has no screen grid. 500ohm shared cathode resistor for both halves of the 6SN7.

A vibrochamp chassis would be ideal, Hammond 260C PT?

You'll need to tweak preamp voltages (say a 500ohm/1K resistor between B+ & preamp/PI node) & probably the NFB loop.

Or PM me, I have a rough sketch of a low power PP amp that you could graft a BF preamp on to.