DALLAS/SHAFTESBURY - 1961-62 combo

[cservonyec]

Dallas progress?

I see you are on tune...


Preamp draw is in working process.

I draw the 1rst gain stage for the two channels (EF86) and need to chek some values in the tonestack.
The tremolo secction remaind untouched....
As said, tremolo is nor working in my amp, and previous owner make some strange mods.

Maybe next year....

Any progress yet with the preamp and tremolo section?
How about some pictures in the meanwhile?
Laszlo.

[chocopower]

... I forgotted this topic. Here a non-finished version of the preamp secction

[cservonyec]

I´m usinf the Selmer schamatic just a base for the real one.
I don´t gonna change any values, except maybe, in the Power supply rail and EL34´s cathode bias resistor. Voltage are really high and need a tweek.

I´m still working in the preamp schematic. As soon i finish the schematic, i´ll post it here. Maybe,it take me weeks, because this is just a free-time hoby.

Ahh! My amp has Tremolo as yours, but it dont work (still....)

stay on tune!!

Chocopower.
It doesn't matter if it doesn't work, or if it was modified. Just trace the connection between the tremolo section and the preamp tube if possible please. You've done such a good job writing out the schematic so far.
Cheers
Laszlo.

[chocopower]

Bufff... i had forgot about this topic (again). Amp had been in the garage for last year... I´m working in it again
. I hope, i could have a definilty schematic in next weeks.

[cservonyec]

Dallas amp.

Better later than never Chocopower. Why do you have it in the garage mano?
You should be playing it. Anyway keep up the good work. And nice to hear from you again.
Cheers

[chocopower]

Hello again!!

i have too many amps (all them older than me, of course).
Now i,m working with this baby again.
I,m gonna use the power secction to build a head. I only have to build the preamp secction in a diferent chasis and put all together inside a head.
this is the schematic (provisional):


The power section is so close to the deluxe 5E3 than need very few mods (just quit the NFB loop and change some values).

The preamp is gonna be something in the Vox-Matchless... way. Still tweaking voltages. Amp is sounding and stable. I just need a little more headroom and it will be ok.

upsss.... i forgott your original requeriment. The schematic for the tremolo secction.... I have been trying to draw and repair it, but this amp had a lot of weird mods from the previously owner. When i received the amp it didn´t sound at all. After make the usual cap job and some others comprobations, everything seems be ok except the tremolo.
the most similar tremolo schematic i had found is this one:



Is a SELMER STADIUM TV19/T.

My idea is build a 18watt power section to use with the original preamp, since i´m gonna use the power secction for the head project.
The original EL34 power secction is too much for the eliptical speakers and cheap wood cab. When i finis the head, i,ll start with the 18watt project. My intencion is get ready the tremolo efect.



regards from Galicia (Spain)

[cservonyec]

Thanks for the reply Choco, my interest in the tremolo section goes as far as how the two tubes were coupled. On the Selmer it is cathod coupled as is the Vox AC10. My dallas amp had almost identical tremolo section as the Voxes, except it wasn't cathode coupled, but the values were the same. But if you have already ripped it apart, it doesn't matter.
What was wrong with the original preamp section for your amp head? It looks preatty good to me. Your plan with the single EF86 in front is not a bad one, but if you need more headroom, why don't you lower the Ra to 100k this will bring down the amplification factor a little bit, and give you more headroom. I see the push pull section has more like a HI-FI amp wiring, you can modify this and change the tubes to 6V6's. They can take fairly high anode voltages, around 400 Volts. Have you considered the Liverpool Trainwreck circuit, worth a try.
Thanks again.
Keep on rocking amigo.

[chocopower]

Hi!

No real problem with the preamp secction. I just whant to learm more about the pentodes and how them react to diferent voltages.

Right now, i´m using a 100k anode load, a 390k screen resistor, with the screen resistor value decresed to .047 and soldered to cathode, not to ground.
A lot more headroom and really nice and punchy basses.
Plate voltage:132v
Screen voltage: 155v


Other combination that really works well is:
The same 100k anode resistor,
but with a voltage divider in the screen with two 470k resistors.
Lightly more gain. and early breakup.
Plate voltage:194v
Screen voltage: 94v

Ah! but the most noticiable improvement was change the semi-dead EL34 screen resistors. I cheked them when i recived the amp and was ok, but now them rise his value to 1k5 and 1k6. I change them for a 1k 5w ones and amp comes to alive!!

Right now, the schematic is semi finish. I´m just playing with the EF86 rotary selector values looking for a more progesive bass cut.

I have tested this amp with 6V6 and work really fine too.
In fact, with the spliter cathode resistors in the power section, i can mix a 6V6 and a EL34 without problems.

I dont want to mess a lot more with it. If i have the amp open in my bench, i can be changing caps and resistor for months.... Amp is good sounding, stable and really practical (30w with 2 el34 , i hate EL84 amps....)

Stay on tune!!!!!!!

[chocopower]

hi there!

it had been a long time, but amp is already finish.

another "hope the last one" schematic:

Green Bullet amp