6V6 5F6A

[Delmar Evans]

Has anyone built a 5F6A driven with a Deluxe Reverb transformer with a 8 ohm OT and s single 12 or two 10 inchers

[bluesfendermanblues]

Yes, I have build a 5f6a using 6v6 tubes and a single 12" 8 ohm speaker.

With below mentioned iron:
​OT: Hammond 125A1A/022640 Dlx Rev (6,6 KOhm/ 20W/ 8 Ohm)
PT:291BEX 125P23D/ 041316 (2x330@0,138; 5v@3A; 6,3v@3A; 50v)

Speaker: Celestion 12G65.

Findings: 2x6V6/1x12@8ohm vs regular 2x6L6/4x10@2ohm:
-Feedback resistor should be 100k with 8 ohm/1x12. (A regular 4x10/2ohm use 27k, and with 2x10/4ohm use 47k).

- PSU: You can use GZ34/5AR4 like in a 6L6 bassman, but I find that a PSU designed for 6L6 will feel a little too sifff with 6v6. Therefore, I prefer 5y3 or 5u4g. And for PSU-caps, in order not to stress the 5y3, I use one 22uf for the B1 node of the supply in stead of 2x22uf.

-The above configurations provide around 388 volts at B1 and the 6v6's are biased at around 22mv (70% dissipation).


General notes on 5f6a's

- Orange drop capss are not the right sound for a Bassman - a little too trebly (great for dumbles, but not tweed fender). I used Mallory 150.

Since the circuit is quite simple, V1 and V3 has a tremendous impact on tone and character of the amp. For V1 I use an old GE12ay7, (but a new JJ12ay7 sounds very similar). For V3 a long plate old Siemens sounds good, (as does a brand new EH 12ax7 LPS).

It pays off to try different tube rectifiers they tend to sound different:
With GZ34 in the PSU the amp sounds dynamic and exiting, but I like it a little browner with a 5y3 or 5u4g. 5y3 tends to sound a little harder in comparison to 5u4G - even though the voltage drop is a little higher with a 5y3.

It's my grab and go amp. We are a 4 piece blues band (bass, drums, harp and guitar). For reharsals the volume is rarely above 10 o'clock - So I use a T-Rex Alberta in order to get the same amount of overdrive, as when playing live where the volume can (sometimes) be push'ed to 4 o'clock. It's a LOUD amp.

[Delmar Evans]

Thanks for the reply, that sounds like the way to go ! Was going to use same power I use for a 5E3 : Magnetic Components Deluxe PT Transformer and Hammond 1750 OT. In addition was going to install a bias pot. I also have some Russian PIO coupling caps that I was going to try instead of Mallory. (unless it is not advised) Are you using a 22mf – 16mf – 16mf for the power supply? Or 22mf – 22mf – 22mf ? I was also thinking of a ½ power switch and I have a vintage Jensen P12N. How does yours sound?

[bluesfendermanblues]

1) IMO, The PIO's are over rated, but try them, maybe you like them.

2) PSU: As per the original 5f6a schematic the PSU caps are:
[20mf+20mf] + 20mf + 20mf + 8mf , (which is fine for 5f6a with 2x6L6)

I use [22mf] + 22mf + 22 mf + 10mf, since the recommended max mf for a 5y3 rectifier is 20mf. I find the 5y3 and the smaller amount of mf a B1 contribte to getting the same response and feel as a 'big' 5f6a bassman - only in a smaller 2x6v6 package.

3) Speaker - I have two reissue P12Q, but didn't like any of them - even after severe voltage treatment (https://tubeamparchive.com/viewtopic.php?t=28952). Too thin and bright for my taste. So in order to get a full and 'natural' sound in the 1x12 package, I went with a 12G65. I'm sure a vintage P12N or C12N is great.

IME using the right speaker unit is more than 50% of the total sound ....and much more important that PIO's vs Mallory 150

[Delmar Evans]

Let the build begin!! Your thoughts on a 1/2 power switch? Also how does it sound? Any clips?

[bluesfendermanblues]

With half power switch, I take it you mean pentrode/triode sw.? unless you like the triode sound, you wont realy hear any difference in terms of perceived loudness.

If you want overdrive at lower levels, use a VVT, but don't sclale the whole amp. put in a master vol and only scale the poweramp.

The only clip I have at hand is a live (iphone) recording from february this year.

https://soundcloud.com/bluesfendermanbl ... easy-opt-8

listen at
1:02
4:44
10:47

Setup: Strat => T-Rex Alberta => 5f6a, 2x6V6, 1x12 (P12Q)