Valco/supro S6422TR

[Tirol29]

Hello !
having lot of spare time cause retired, i started last year to build a tube amp.
i wanted not too loud but with caracter, and i found Uncle Doug's  Valco project.
i had until then a Faylon Studio (100w) too powerful and very heavy, i gave it to my niece who started playing bass
after that i bought in '93 a Marshall 8080, sold 2 years ago.
Having only a Vox mini 5 for studying/training i wanted something much more reliable for my LP custom'92 and
my Mustang competition orange '72. thus here we are....
components came from worldwide : USA, Germany, France...
First, preparing the chassis to dimension the cabinet :

Then making the cabinet with staight tails jointed using my table saw following this method
https://www.youtube.com/watch?v=kbgnnsilyxM
here the result :

then rounding all edges using my homemade router table

again with the router table preparing the speaker (Jensen 10") frame

now before continuing on the cabinet, as all electronic parts received, started the job i was
trained to as electronic bachelor in my younger life


all completed, speaker temporlarly connected, i fired up and Deo Gratias nothing exploded , sound was there but not as expected. The 12AT7 was blueshing, then  i contacted the vendor and he sent me without discussing another one.
another problem came from the reverb footswitch : nothing very important just a bad mounting of the RCA plug
one bad out of 4 ...
Now time came to finish the cabinet
Easy first the grillcloth of the speaker frame


then the hardest : tolexing, no mistake allowed

here the finished cabinet with its vintage like handle




all done !

this was a very pleasant time doing this project, even if a bit expensive.
less expensive were 2 6V6GT i had from an old fellow who was the seller of the Faylon and the Mustang in the '72; when i asked him how much ? he replied : "nada, that's rubbish nobody uses that now".
cheers,
Roland

[EL34]

Posted in wrong board
moving..............

[Tirol29]

my bad... first post first mistake
thanks

[ac427v]

Beautiful work. I want to do that!What grill cloth and tolex did you use?

[sluckey]

Nice project. Great workmanship! Thanks for sharing.

BTW, I've never seen the S6422TR. Could you post the schematic?

[66Strat]

Very nice work!

[DummyLoad]

very nice!

--pete

[kagliostro]

 

Franco

[Pietro]

very nice!

but is the sound to your liking? 

[Tirol29]

Beautiful work. I want to do that!What grill cloth and tolex did you use?

tolex is Navy blue
grillcloth is Fender blue-white-silver
both found at Tube-town Germany

[Tirol29]

BTW, I've never seen the S6422TR. Could you post the schematic?

here you are 
original from Valco :

then from Uncle Doug mods from UD are in red :

do not take into account voltages. for example V3 has 2 differents values for cathodes 
UD used a friend's talent for all drawings  including lay-out :


cheers,
Roland.

edit :
i added 2R of 100 Ohms at the pilot light as virtual CT
Pot for reverb is with a switch for the time i didn't bring the footswitch 

[bmccowan]

Wow - super project! You even used the typical Valco terminal strip approach. Did you make that faceplate? Nice.

[Tirol29]

Hi 
i've one question for one amp guru 
i like very much the sound of this amp, although i have very little issue with the tremolo
when intensity is as full but i suspect bad pot....
Question is not that but as i don't use low input with my guitars i was wondering, as read here and there, if  i will benefit of the V1 spare triode to wire a "parallel" input channel.
What will be the best ? :
1. each input  leads to its own grid with 33kR, both triodes sharing same RK and CK, input one being as to-day (one triode), input 2 being "parallel" triode, playing with jack switching;
2.same as above but for the second triode different Rk and Ck (or no Ck),any way to change more ?
3.instead of input jack 2, use a switch or a footswitch
what will give me some enhancement or do i spend end of year festivities (and following years) just forget all of this ?
thanks for reply
in counterpart , i will give you accurate voltages, and some recording.... (joking...)
Roland.

[shooter]

fwiw
here's the plexi6V6, what I like, each can be flavored once you get it working, they mix nice for a "3rd" flavor.

https://el34world.com/Hoffman/files/Hoffman_Plexi_6V6-V2.pdf

If you want the more "traditional" parallel you'll have to hunt it down 
I would recommend using separate cathode parts in any choice

[Tirol29]

If you want the more "traditional" parallel you'll have to hunt it down 

thanks Shooter,
asked for a Guiness and got an IPA 

[shooter]

I prefer dirt grown herbs myself

https://el34world.com/charts/Schematics/files/Matchless/Matchless_chieftan.pdf
split up the cathode otherwise, traditional version for your IPA 

[sluckey]

Before you really commit to anything, give this a try. Very quick and easy...

Put a jumper between pins 1,6 and 2,7, and 3,8. Nothing else.Should look like V1 in this circuit...

     http://sluckeyamps.com/Dual_Lite_(British).pdf

Or, for a bit more options, do it like V1 in this circuit...

     http://sluckeyamps.com/Marshall_18w.pdf

[Tirol29]

thank you guys 
Sluckey, since i will plug my iron i will go for the second choice which has the advantage to compare the two situations.
but i don't have 1Mohm resistor, old fashionned electronic stores don't exist anymore i will have to command through the net 
As promised  i noted the DC voltages :
B1=366v ; B2=361v ; B3=302v
V1(7025)  P1=227v  K3=2v
V2(12AX7) P1=190v  K3=0,4v ; P6=302v K8=2v
V3(12AT7) P1=P6=362v ; K3=K8=7v
V4(12AX7)  P1=176v K3=1,1v ; P6= 190v K8=1,6v
V5(6V6) P=364v Gs=361v K=23,6
   RK=752Ohms  => Ps = 11,4W 
[edit] a bit hot ?
Mazda Belvu and 6v6GT prints almost gone.... [/edit]

[Tirol29]

hello all of you,
i received the 1meg resistors and then will be at the edge to start.
But first i have to say, after read lot of topics, that i'm very impressed with how all of you, tube gurus, give so much time and even patience to give every answer to every question   
i don't know if i will get something more positive in doing this mod on an amp which just replies to mt expectations; but try and see...
that's not the end , i've some questions 
1. what will be the behavior of V1 with a common 100k for plate load, does that mean as current must be doubled (?) that the real voltage on both plates be half as actual, then output as well ?
2.connecting pin 5 to feed second heater will make second cathode to spray more electrons in the cloud ? are these shared with both plate/cathode duality  or to all ?
3.is there any usage or not for the 68K (i will // to get 34k ) ?
for shooter :

cheers folks,
Roland.

[shooter]

Now that's my kinda music , thanks

here's my stab at the ?'s

the "34k" I view as "best practice" part, mounted at or real close to the grid

the filament ? is confusing, did you only wire it for 1/2tube originally ?

the 100k gets all the current for both tubes, another best practice thing is too build with flame-proof 1W metal film so if that's your case, it's already "sized correct".  It's always worth the time to measure the volts and crank out the math, jusssst in case that 10k got slipped in by mistake   

[Tirol29]

hello all 

the "34k" I view as "best practice" part, mounted at or real close to the grid
in my mounting they are at the jack level, but as a lot of shielded wires, amp is dead quiet as you say.
i've read the grid stoppers are more here for a RF filter, associated with inner capacitance of the tube

the filament ? is confusing, did you only wire it for 1/2tube originally ?
yes
the question was more about interference the triode each others inside the same bulb
existentialism, forget it...

the 100k gets all the current for both tubes
in fact here the plate load for DC is 270K. i was wondering if using the same plate resistor for both triodes will change the plate voltage and thus the load line of the amplification, thing i'm not very familiar with, in final the output amplitude.
My concern is if that schematic, as the 18w of Sluckey , offers a lowered output in the single input, and the same as today with the parallel input, there is no gain, just a bit over consumption on 6,3v por nada .
another point is tremolo woggle comes here in the cathode of V1 and is a very nice feature easy to modulate.Should this continues with the mod 

in a previous post i gave the voltages.
and there was a question about power dissipation of the 6V6, if a bit hot?
Amp cranks well with HB about vol at 7 or 8 not before, quiet enough room at my taste...
that's not a gig warrior i wanted   
if all of your answers are just stay as you are, it's fine for me, but i want to know more from you !
Rol.

[Tirol29]

Hello :)

today i've made the mod using the parallel triode as V1 had one triode free.
i've made the same wiring as Sluckey shown here marshall 18W
i've just kept the 68kohms, i don't think it's make a big diff against 33K or 10K...
also kept  the 270K plate resistor common
cathods  just jumpered
Try with humbuckers guitars, a bit of more level but not something to touch the seventh sky...
maybe because it's only about 5W amp
will try another day with my Mustang and my acoustic Yairi

[Tirol29]

hello,

a "little" question 
output tube is a 6V6GT from Mazada-Belvu, the  datasheet indicates that with load resistance of 8,5K we get 5,5W .
at this time Vp= 364v, Vk=23,6v with Rk=750R which gives 10,8W power dissipation (assuming Is about 6% of Ik with Ik=Ia+Is) and connected to the 5K wiring of the OT (Classic Tone 40-18031)
will i gain 1W if i connect to the 8k wiring ?
tks for answering,
Roland.

[shooter]

will i gain 1W if i connect to the 8k wiring

quick math says you're dissipating ~ 11W
If you have the tap available try it, won't hurt anything.  spending money for 1W might hurt 

I would expect plate B+ to increase slightly when it's "most efficiently" coupled but that gets wonky over the whole spectrum.

[shooter]

if all of your answers are just stay as you are, it's fine for me

you're probably within the realm of, there's not much left too do.
you can tweak tone, the 1st place for that besides guitar is speaker.  my 4W 5C1 became a completely different beast when played through a Marshall 4 X 12 cab

bottom line, play it awhile, pedals, speakers then except it is what it is.

dave

[PRR]

Try the 8k tap. On paper it loks a little better, but not a WOW! difference. Real life may be different.

[Tirol29]

thanks for the answers,

Try the 8k tap.

will do....  as very bad weather no way to start gardening

If you have the tap available try it....

yes there is  see my post 

[Tirol29]

hello all,
made the mod on the OT and yes there is a bit more power, a bit... but there 
tried with my Mustang and yes the paralleled input triodes (7025) makes a lot with these old PU's ('72)
question for Sluckey:
when pushed (intensity after 3/4 way) tremolo alters the sound but i think that's normal, no ?
halfway both speed and intensity, that's very cool 

[sluckey]

when pushed (intensity after 3/4 way) tremolo alters the sound but i think that's normal, no ?

I can't recall if mine acted like that. Sounds like you may have more intensity than you really need. Did you do the INT pot the same as I did? What value pot?

[Tirol29]

for this part of the build i've followed stictly the UD's schematic post #10 above
V2 is 7025, i've tested also with ECC83S: same
the pot is reverse audio.

[sluckey]

I believe you just have more intensity than you need. Cheap easy solution... don't turn up past 75% if you don't like the sound of overdriving tremolo modulation. Or, increase the value of that 3.3M resistor. Or, use a 100K-L intensity pot.

Changing the pot or resistor will have the same effect as not turning up so high with your current circuit.

[Tirol29]

tks,
i don't remember why i've put an antilog will change for linear, idem for the speed pot  log -> lin

[sluckey]

tks,
i don't remember why i've put an antilog will change for linear, idem for the speed pot  log -> lin

Probably because Fender uses reverse audio taper for speed and intensity.

[Tirol29]

Probably because Fender uses reverse audio taper for speed and intensity.

and more probably because i didn't know that 

[sjwood3]

I just picked up one of these, chassis only, today.   Next project.  Next project, behind the other 4.   I love this forum.