Well, I try one other time ("5C1" with OD) - Please need councils

[kagliostro]

This is one other way I've think to arrange my stereo SE guitar amp (that uses recovered materials)

It remember a bit the 5C1 but the gain of V1 is tamed using a 39k plate resistor for V1 and a Tone Circuit (that will eat some gain)

on V2 I've think to use a split plate resistor (with a trimmer to be adjusted at taste)

the values for the polarisation of V1 (and V2) are catch from this schematic

http://www.bensykora.com/7cylinder/7cylinder_final.gif

here the source (with samples of the sound of the amp)

http://www.bensykora.com/7cylinder.html

and here is my arrangement with 6ak5 and el95 tubes



the power section is copied from a PP DOUBLE SE ELL80 circuit used in the old Grundig radio of which I salvaged the PT - OT and elliptical speakers

but I'm not sure if the cathode resistor is good at 400R, as I draw, or it will be better a 320R as indicated on datasheet

Thanks for any advice about the plan and about the OD stage switch

K

[kagliostro]

Errr.... no, that isn't an UL connection, the portion of OT winding is used by Grundig as a choke for G2

look to the schematic, an UL connection has G2 connected in the "middle" not on one side of the OT

in this arrangement (often used on old apparatus) B+ is connected in the "middle" intake then the opposite side is the plate connection

and the nearer side is the G2 connection

Is a way to have less noise

Franco

[kagliostro]

A friend pointed me to a big mistake I do on the schematic, I forgot to draw the coupling cap between the OD tube and the Power Tube



K

[DummyLoad]

I was surprised to see an ultralinear connection on a single ended amp.   I then did a search for s e amp ultra linear. 
Hammond makes and sells a series of UL SE o/ts.

Nice upgrade for SE amps.

that's for hum-bucking for g2. it IS SE single tube class-A and it's not a UL tap. notice that B+ is at CENTER. g2 is at end of winding, plate at other end of winding. in SE single tube class-A the UL tap is at CENTER, B+ is at end of winding, plate at other end. 


--pete

[kagliostro]

Thanks Pete

you have explained it much better than I did


Franco

[DummyLoad]

285V - 22V (estimated cathode bias voltage by tossing darts on datasheet curves),if you end up with 263V anode to cathode and 12W is max for 6aq6, then 10.8W is where you need to idle at (90% of max.) 10.8W/267V ~41mA. so Rk is then 22V/41mA ~536R

start with a 560R and fine tune there. remember to calculate the dissipation by measuring voltage from anode to cathode, measure the voltage across the cathode resistor and calculate Ibias. you'll probably ends up with a 470R 5W resistor.

it doesn't have to be exactly 10.8W: 10W or even 9.5W is still ok. settle where you are comfortable the tube isn't going to red-plate and sounds best.

--pete

[kagliostro]

Ciao Pete, thanks

you refer at 6aq5 and 6aq5 is an el90 tube, not an el95 tube

http://tdsl.duncanamps.com/link.php?target=002583E6

http://www.r-type.org/pdfs/el95.pdf

I've some 6aq5 tube, but the OT is for 1/2 ell80 that is exactly the same of an el95 tube

Franco

[DummyLoad]

Ciao Pete, thanks

you refer at 6aq5 and 6aq5 is an el90 tube, not an el95 tube

http://tdsl.duncanamps.com/link.php?target=002583E6

http://www.r-type.org/pdfs/el95.pdf

I've some 6aq5 tube, but the OT is for 1/2 ell80 that is exacrly the same of an el95 tube

Franco

sorry franco,  my apologies.


--pete

[kagliostro]

Why ? No reason to apologize 

it is easy to swap one tube for the other

those tubes are a bit odd

Many thanks for the interest and answering

Franco

[DummyLoad]

90% of 6W ~ 5.4W - Ibias ~ 5.4W

B+ = 285V

darts on curves show about -11.4V at g1 @ 275V Va.

Vanode ~273V so Ibias ~ 5.4W/273V ~ 21mA

with 11.4V/21mA Rk is estimated to be 581R

use a 560R 2W part: bump to 600R 2W if needed.

--pete

[kagliostro]

Wow, 600R is near two times what is indicated on the datasheet for Class A 250v B+

http://www.r-type.org/pdfs/el95.pdf

I think that without your aid I would have fried the tubes in a few times 

Thanks Pete

Franco

[DummyLoad]

franco, that's 560R per tube.

--pete

[kagliostro]

OK, 560R, that is way far from my 400R

Thanks again 

Here the revised schematic with the new cathode resistor and only one relay (a friend told me that only one relay is enough)




Franco

[Ed_Chambley]

What is the reasoning behind the MOSFET?

[DummyLoad]

it's VVR. this is a low watt amp already, IMO it's a waste of time and parts.


--pete

[kagliostro]

Yes, also thinking to a stereo (as the amp is planned to be), the VVR is excessive


Thanks for pointing it





Franco

[Ed_Chambley]

Just watching.  I have a 5C1 and I like this.  Thanks for posting it.  I have been thinking of modding it a little.  It is a build BTW, not a original.

I see it as a VVR now.  I agree, it really doesn't need one.

[kagliostro]

This, I think, in an SE amp is an improvement



a capacitor multiplier reduces considerably the ripple

Franco

[kagliostro]

The grid stopper is already present, what is missins is a leak resistor and ... that is one other thing I forgot, thanks for pointing it

On the Grundig schematic there is a 1.8M leak resistor, now added

I would consider disabling the OD tube if possible when not in use

Any idea about how to do it ?

About the capacitor multiplier I've seen examples that it was used for both preamp and power amp

the schematic of the capacitor multiplier isn't flavour of my bag, I copied it as is



The two OT are from an old Grundig Como Stereo Radio, I've somewere more details about them, when I find it I'll post

The 220k resistor in parallel with the 33uF cap is a bleed resistor, his purpose is to discharge quikly the electrolytic