Fender Deluxe Reverb reissue - save the power tubes

[CJ]

muddy sounding amp,  power tubes bombed up and depleted,

replace with groove tubes 6V6R, as opposed to 6V6C which are made in China, R means Russia, same tube as Electro Harmonixx,

great sounding tubes but one starts to red plate after ten minuets idle, wtf?

dang Deluxe Reverb 415 plate voltage,  new tubes not like RCA,

re-bias cold and watch the bias drift, no good,

install 2 ea. 1 K  7 watt resistors, screens down from 412 to to 384,  helps a lot, but sill a little drift,  install 47 ohm cathode resistor,

happy day , no drift, better tone with a little NFB, 

so a two part solution, add screen  supply resistance, add cathode resistor-game over.

 

[CJ]

load line now below max plate disp. 

can drop bias down and run current at a warmer level,  42.5 ma , 21 ma per tube,  about 65% of max disp.

tubes should last longer, and the amp sounds better,

 

[alexc]

I just finished a pp 6V6 guitar amp with a Magnetic Components  'classictone 15W' deluxe style output traffo .... Edcor psu traffo, sino choke, JJ multicaps and a russkie 5Z4P rectifier tube.

I used a pair JJ 6V6S with cathode resistance bias - they are max rated for 500V plate and 450V screen with plate dissipation of 14W.

JJ 6V6S spec sheet  ...  http://www.mif.pg.gda.pl/homepages/frank/sheets/163/6/6V6S.pdf

Have 425V on the plate and 395V on the screens and idle is around 9.5W dissipation.

No probs at all with bias drift or runaway current, although I did find the output traffo to be of a lower primary Z than expected - I had to use 8ohms speaker on 4ohm tap to get reflected 7.5K-ish  plate-plate.

Using a 6SL7 up front and a 6SN7 as a cathodyne with variable nfb - these are both modern tungsol tubes.

I get 3% thd mostly H2 at 12Wrms into 8ohms when it's dialled in for low distortion in 'triode mode'

I can get that up to 15W with 7%  and beyond using the 'gain' and 'nfb' controls in 'pentode' mode

Sounds very good ...  performs 'better' than when I had it set up for nos 6v6gt (60s GE with lowered supply voltages).

I have it playing thru an old Bell&Howell sealed back speaker cab with a new Jensen 'mod' alnico 12" 8ohm speaker.

Works great for getting some honest 'growl' at lounge room volumes, with enough juice on tap to get a little scary   I'm playing it with an SG and some fairly hot emg hz passive ceramic pups right now  8)

Reasonably cheap ...  maybe 500usd or so all up.

 

[alexc]

Me being me, it also has a line amp with a nice balanced output  - a utc A44  traffo 4K/600 ohm taps.

Its a totem style cathode follower using a nos GE 6U8A tube (pentode top, triode bottom) and is driven by a russkie 6N2P  allowing it's own  'level' control and some local nfb as well.  (the 6N2P is a little ragged at 3.65% thd)

...  allows me to balanced send either the speaker signal, or a front panel aux input or a sum of both 

I'm just buying a few more parts -  a second psu filter choke for the preamps/PI  and a new JJ 5751 to replace the 6N2P; also I'm moving to a pair of  JJ 4 section psu caps.

...  then to  rip it all up and redo it over ..  with some changes and a much improved layout  ..  to get it really really good!

 

[bluebird]

Awesome alexc! Love the line out with some iron in there...I can hear the rock n' roll ;D

 

[alexc]

Thanks 

I don't think there is much in it, sound-wise or even power-wise,  with the higher voltage plate/screen (6V6 permitting)  ...  just a little lower distortion.

I just happened to have an Edcor PSU traffo that was quite a bit higher than the Fender Deluxe spec and didn't want to overtax my nos GEs (as CJ describes above)  or do the dropping power resistor thing on the B+.

And I was curious to try the JJs, which were about 40% the cost of the GEs.

I have to say I really like the JJ 6V6S a lot -  my first time with cathode bias - especially with the octals in the preamp/cathodyne.

I'm getting some smooth onset of THD in the preamp and the finals are very touch-sensitive and with a nice bit of compression when pushed 

I can do without the 'fizz' that one can get all too easily with AX7  gain stages and  cathodyne.

So, my first Deluxe build is getting a lot of use and pushing the Super Reverb out of the 'lounge'  8)

 

[fazer]

Thank CJ and Alex for the insight.
I have a 6g3 fender and just don’t use much with the old sovtec 6v6 tubes.  Think it’s the tubes but the voltage is about 370v if I remember correct .  I’ll get it out and play with it today.

Alex I would love to hear the gradual onset of distortion with some MP3 clips if you have any in that hi if looking version Of a deluxe .
I have an old standel artist with a working power amp section.  Currently has el84s in it.  I was thinking ac 15 but I replaced the caps in the voltage doubler with new 100 u and the doubler output went from 360v to 400v.  That made me think about replacing el84’s to 6v6’s. Now with the new 6v6’s  I think about making them not red plate and like CJ’s. Stabilizing procedure. 

 

[alexc]

Too late! I already started the 'rip up'  for the  new layout.

Nothing very special about the circuit, however :

- 1st  6SL7 stage with a fairly high plate resistor of 150K and a bypassed bias of +1.5V, feeding a 2-knob tone stack of high Z with 500K  'gain' pot

-  2nd 6SL7 stage biased to unbypassed +2.5V with a 100K plate. That feeds a and a 2:1 divider with a 500K 'vol' pot

- 1st 6SN7 stage with a 58K plate load bypassed +4.0V bias, 300ohms fixed + 1K lin pot for nfb into cathode. I use a 'step network' for dc coupling into the cathodyne phase splitter

- 2nd 6SN7 splits with 22K resistors biased for around 100V on the grid and 104V on the cath (has dc raised ac heaters)

- finals are adjustable cathode bias with a triode/pentode switch (large DPDT HV capable toggle)

The smooth THD onset is a result of the interplay of the 'nfb' control and the 'gain' control. The main 'Vol' control is mostly all the way up!

The basic character is set by the triode/pentode switch - Triode mode sounds a lot better to my ears, being very smooth - but it needs higher gain in the preamp - so here the 'gain' control compensates nicely.

The variable nfb control is the 'magic' - but to fully realise it, one needs very low hum throughout.
That's the reason for the large-ish plate resistors in the preamps, to maximise power supply rejection ratio (psrr).

It's also why I am using a second filter choke to further knock down HV ripple in the preamp stages. On top of that, I have 5 stages of C-R filtering for HV.

Furthermore, the high HV rails throughout tend towards less distortion - SL7 is operated at 300V, the 6SN7 at 400V, the finals are 420V plates and 390V screens for pentode mode and both 420V for triode.

I think some more 'tone shaping' can be achieved to further smooth things out with some judicious filtering in the preamp stage couplings and also on the nfb line.

Also the speaker cab plays a big role - I favour a sealed cab for more 'thump' in the chest impact at the lower end, and a 'later' breakup in the speaker - the jensen 'mod' 12" alnico is fairly 'affordable' 50W unit.

I prefer the 6V6 with octals to EL84 with novals  myself, although I do have a nice el84 amp too!

For a rugged EL84 try the russian 6P14P - it's an affordable el84 type with higher plate ratings of 400V/14W and a decent screen dissipation as well.

ANyways, that achieves my goal of smooth breakup and avoids the 'fizzy' preamp type of distortion that I dislike. Transistor overdrive pedals do so much better a job, imho, for that stuff.

I like to get a 'growl' in the lower registers, when 'digging in' with the tops fairly clean. I generally go for 3% thd max as a 'tuning' goal at most volumes with the capability to drive more THD as required.

Of course, with everything right up and nfb down, the think becomes a monster distorted beast ...  if one is into that sort of thing! 

 

[fazer]

Cool !!  I got my 6g3 out and plugged into a 2x12 Vox bottom.  I’ve never cared for a 12 single in that brown vinyl open back. Cab is solid pine .  I like a 12 “ EVM is semi full sounding.
The box has 2 Celestine H30’s from 1972 vintage.  I’ve always liked their sound.  The deluxe sounded great recorded today.  Very organic .    I jam with my brother on drums on Sundays in the winter.  Lots of fun.  My 50watt amps are to loud.  I have power soaks but amps should fit room. Anyway I’m thinking of getting a power transformer to get. 315 -325 b+ for el84s and a tube rec.

 

[alexc]

'amps should fit the room' 

That just about says it, I think     A pair of 6V6 or EL84 just about does most situations, I think.  10 to 15W max.

A pair of 6L6s or even EL34s with plenty of speaker real estate is *very* loud in a confined space.  I rarely get my super reverb beyond '3'  Those 4x10s really get the air moving!

I like a 'head + cab'  arrangement to get my variation in sound. Sometimes a 15" open back pine cab, sometimes a 4x10" open pine but mostly now a closed single 12".

Nowadays I find it hard to believe I used 100W quad 6L6 tube amps with a couple of 2x12" closed back cabs for most of my younger days ... what was I thinkin 

SO - a lot to be said for the good ol' AC15, Deluxe and Marshall 18W  'ers,  done as CJ describes - with original specs and voltages.

 

[CJ]

use to play a twin reverb into a pair of Altec 417-8C's in the bedroom on 10  what was i thinkin?

no wonder the teeth are fallin out,