Any 8X El34 amps here?

Bernardduur · 10-17-2009, 06:34 PM

I got this old Jamm amp in which has 8x EL34. I don't like the original schematic so I was looking at other schematics on 8x EL34 amps.

Can't find any; any help?

Alf · 10-17-2009, 07:05 PM

Can you show the original schem first ?

And some phots of the guts would be nice ; must be a huge OT.

Bernardduur · 10-17-2009, 09:59 PM

Quote:

Originally Posted by Alf

Can you show the original schem first ?

And some phots of the guts would be nice ; must be a huge OT.

I'll make the schematic digital soon! it is part SS (preamp) part tube (PI, buffer and output).....

Thing is HUGE! Biggest transformers I've seen; the choke is bigger then most power transformers

black_labb · 10-18-2009, 02:04 PM

what are you trying to achieve by looking at a schematic for an amp with 8 el34's? its just like an amp with 2 but 4 sets of 2. (so double one with 4). its the same circuitry in parrallel. just takes a bigger transformer as you've noticed.

sounds like an interesting amp though.

Bernardduur · 10-18-2009, 02:28 PM

Quote:

Originally Posted by black_labb

what are you trying to achieve by looking at a schematic for an amp with 8 el34's? its just like an amp with 2 but 4 sets of 2. (so double one with 4). its the same circuitry in parrallel. just takes a bigger transformer as you've noticed.

sounds like an interesting amp though.

I've worked with these kind of amps before and they all had buffers set between the PI and the powertubes (tube buffers); I just wanted to know if that was nessecary or what designs were used in this.........

PICS!!!!!

mooreamps · 10-18-2009, 06:48 PM

Quote:

Originally Posted by Bernardduur

I've worked with these kind of amps before and they all had buffers set between the PI and the powertubes (tube buffers); I just wanted to know if that was nessecary or what designs were used in this.........

PICS!!!!!

There is no reason why not having a tube buffer between the PI and the power tubes.

Bernardduur · 10-18-2009, 06:54 PM

OK, so it'll behave just like a normal amp but then just with more tubes. Great!

Schematics:

PSU

Poweramp; only drew 2x EL34

Preamp

Alf · 10-18-2009, 08:59 PM

Bernard,

Could you post the preamp in a bigger resolution, the values are illegible.

So it has a transistor preamp ! Where is the other half of the ecc83 before the PI ?

tedmich · 10-18-2009, 09:43 PM

what a monster!

SS preamp and 100w brute watts output...kind of an inverse bedroom amp...

not quite what I am looking for but to each there own!

Bernardduur · 10-18-2009, 10:20 PM

Quote:

Originally Posted by Alf

Bernard,

Could you post the preamp in a bigger resolution, the values are illegible.

So it has a transistor preamp ! Where is the other half of the ecc83 before the PI ?

Preamp, now bigger

The other half of the ECC83 is not used.

The PI tube is an ECC85 tube. No heater on pin 9 on this tube. Why was this done? Is the ECC85 a nice PI tube?

Alf · 10-19-2009, 02:44 PM

The ecc85 for PI is a good tube it can deliver more current than a ecc83/ 12ax7 and pin 9 is a shield between the two triode halves.

I don't know what the function is of those diodes at the front of the preamp . Beats me, can't be clipping can it ?

Alf

Bernardduur · 10-19-2009, 08:01 PM

I've seen this kind of clipping before as a method of compression.

I'll make a part of the schematic again; clearly I can spot some changes that were made after the PCB was made. Dunno by who

black_labb · 10-20-2009, 12:38 PM

Quote:

Originally Posted by Bernardduur

I've worked with these kind of amps before and they all had buffers set between the PI and the powertubes (tube buffers); I just wanted to know if that was nessecary or what designs were used in this.........

PICS!!!!!

ahh, makes sense. buffers tend to be used in more hifi designs (meaning amps where fidelity is desired). with more output tubes you would probably want a lower impedance feeding them, but when it causes a problem i dont know. a PI tube that can feed more current (ecc85 compared to a 12ax7) is a good start as they tend to have a lower output impedance in most cases.

Bernardduur · 10-20-2009, 09:08 PM

Quote:

Originally Posted by black_labb

ahh, makes sense. buffers tend to be used in more hifi designs (meaning amps where fidelity is desired). with more output tubes you would probably want a lower impedance feeding them, but when it causes a problem i dont know. a PI tube that can feed more current (ecc85 compared to a 12ax7) is a good start as they tend to have a lower output impedance in most cases.

Tnx! A simple cathode follower as used in older Fender studio models have my interest so I'll try em!
For the others, here's how the preamp's input was set up: Picture

Albert Kreuzer · 10-20-2009, 10:46 PM

Quote:

Originally Posted by Bernardduur

I've seen this kind of clipping before as a method of compression.

To me it looks more like input protection for the FET.

Cheers,
Albert

PS: I have an old "LAY Power Block" lying around with 10 x EL34

Haven't opened it up yet. IIRC it has an ECC81 LTP inverter.

Bernardduur · 10-20-2009, 10:48 PM

Quote:

Originally Posted by Albert Kreuzer

To me it looks more like input protection for the FET.

Cheers,
Albert

PS: I have an old "LAY Power Block" lying around with 10 x EL34

Haven't opened it up yet. IIRC it has an ECC81 LTP inverter.

Could be! It'll add some compression when the signal gets too hot or even clips it.

Alf · 10-21-2009, 04:46 PM

Imho I think this circuit was designed for playing (or passing) a clean signal, so who wants clipping at the front then ?

I would remove it .

What is the inductance of the choke ?

Alf

Bernardduur · 10-21-2009, 04:50 PM

Quote:

Originally Posted by Alf

Imho I think this circuit was designed for playing (or passing) a clean signal, so who wants clipping at the front then ?

I would remove it .

What is inductance of the choke ?

Alf

The signal has to be higher then the threshold of 1.4V to get clipped; in this setting it'll protect the FET. I'd rather use an end to end diode setting with one end to ground, one end to V+ as it is normally done.

Can't read inductance here; no Henry on my DMM

Bernardduur · 10-24-2009, 08:45 PM

Question:

I've seen most amps work with simple caps to ground as power supply filtering.... now this amp has bleeder resistors over em. What is the advantage of that?

link to pic

black_labb · 10-26-2009, 02:33 AM

bleeder resistors discharge the caps after power off so they dont stay at high potential for long periods of time.

Bernardduur · 10-26-2009, 08:41 AM

I found in a good source that they are also used as ways to get both caps the same load so not one is quicker then the other. Makes the 'new' value (2 caps in series) more stable.

My question is more on the soundwise; how is it compared to the standard cap to ground? I think I'll swap em for 47uF caps as I can get em in the right voltages pretty easy.

harry · 10-30-2009, 11:27 PM

can anyone explain that to me? i've always wondered why.

surely two identical capacitors would have the same resistance?

is it just because the resistance of the capacitors is low, so resistance in wires etc. would affect the potential divider that's created by the capacitors?

black_labb · 11-02-2009, 08:17 AM

Quote:

Originally Posted by harry

can anyone explain that to me? i've always wondered why.

surely two identical capacitors would have the same resistance?

is it just because the resistance of the capacitors is low, so resistance in wires etc. would affect the potential divider that's created by the capacitors?

not sure exactly, but probably an issue with tolerances. the caps may age differently or have different temperatures when set up. putting resistors in parallel with them ensures that there isn't a problem

Bernardduur · 11-08-2009, 02:14 PM

Quote:

Originally Posted by black_labb

not sure exactly, but probably an issue with tolerances. the caps may age differently or have different temperatures when set up. putting resistors in parallel with them ensures that there isn't a problem

Great!

10-17-2009, 06:34 PM	#1
Bernardduur Senior Member Join Date: Apr 2007 Location: Nijmegen, Netherlands Posts: 110	Any 8X El34 amps here? I got this old Jamm amp in which has 8x EL34. I don't like the original schematic so I was looking at other schematics on 8x EL34 amps. Can't find any; any help?

10-18-2009, 06:54 PM	#7
Bernardduur Senior Member Join Date: Apr 2007 Location: Nijmegen, Netherlands Posts: 110	OK, so it'll behave just like a normal amp but then just with more tubes. Great! Schematics: PSU Poweramp; only drew 2x EL34 Preamp Last edited by Bernardduur; 10-18-2009 at 07:58 PM.

Thread Tools
Show Printable Version Email this Page
Display Modes
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
RCA 8x-71	lowell	Music Electronics	12	04-25-2009 12:27 PM
EL34 to KT66?	rockon1	Mods & Tweeks	5	12-23-2008 04:50 PM
EL34 vs 6V6	daz	Theory & Design	8	06-25-2008 08:58 AM
Best EL34 reissue?	fuzzman93	Guitar Amps	1	02-19-2008 04:35 PM
EL34 and EL34B help	matatak6	Guitar Amps	4	02-28-2007 11:59 AM

10-17-2009, 07:05 PM	#2
Alf Senior Member Join Date: May 2006 Location: Netherlands Posts: 120	Can you show the original schem first ? And some phots of the guts would be nice ; must be a huge OT.

10-18-2009, 02:04 PM	#4
black_labb Senior Member Join Date: Apr 2007 Location: sydney australia Posts: 736	what are you trying to achieve by looking at a schematic for an amp with 8 el34's? its just like an amp with 2 but 4 sets of 2. (so double one with 4). its the same circuitry in parrallel. just takes a bigger transformer as you've noticed. sounds like an interesting amp though.

10-18-2009, 08:59 PM	#8
Alf Senior Member Join Date: May 2006 Location: Netherlands Posts: 120	Bernard, Could you post the preamp in a bigger resolution, the values are illegible. So it has a transistor preamp ! Where is the other half of the ecc83 before the PI ?

10-18-2009, 09:43 PM	#9
tedmich Senior Member Join Date: Apr 2008 Location: PDX Posts: 371	what a monster! SS preamp and 100w brute watts output...kind of an inverse bedroom amp... not quite what I am looking for but to each there own!

10-19-2009, 02:44 PM	#11
Alf Senior Member Join Date: May 2006 Location: Netherlands Posts: 120	The ecc85 for PI is a good tube it can deliver more current than a ecc83/ 12ax7 and pin 9 is a shield between the two triode halves. I don't know what the function is of those diodes at the front of the preamp . Beats me, can't be clipping can it ? Alf

10-19-2009, 08:01 PM	#12
Bernardduur Senior Member Join Date: Apr 2007 Location: Nijmegen, Netherlands Posts: 110	I've seen this kind of clipping before as a method of compression. I'll make a part of the schematic again; clearly I can spot some changes that were made after the PCB was made. Dunno by who

10-21-2009, 04:46 PM	#17
Alf Senior Member Join Date: May 2006 Location: Netherlands Posts: 120	Imho I think this circuit was designed for playing (or passing) a clean signal, so who wants clipping at the front then ? I would remove it . What is the inductance of the choke ? Alf

10-24-2009, 08:45 PM	#19
Bernardduur Senior Member Join Date: Apr 2007 Location: Nijmegen, Netherlands Posts: 110	Question: I've seen most amps work with simple caps to ground as power supply filtering.... now this amp has bleeder resistors over em. What is the advantage of that? link to pic

10-26-2009, 02:33 AM	#20
black_labb Senior Member Join Date: Apr 2007 Location: sydney australia Posts: 736	bleeder resistors discharge the caps after power off so they dont stay at high potential for long periods of time.

10-26-2009, 08:41 AM	#21
Bernardduur Senior Member Join Date: Apr 2007 Location: Nijmegen, Netherlands Posts: 110	I found in a good source that they are also used as ways to get both caps the same load so not one is quicker then the other. Makes the 'new' value (2 caps in series) more stable. My question is more on the soundwise; how is it compared to the standard cap to ground? I think I'll swap em for 47uF caps as I can get em in the right voltages pretty easy.

10-30-2009, 11:27 PM	#22
harry Senior Member Join Date: Jul 2007 Location: leighton buzzard, uk Posts: 113	can anyone explain that to me? i've always wondered why. surely two identical capacitors would have the same resistance? is it just because the resistance of the capacitors is low, so resistance in wires etc. would affect the potential divider that's created by the capacitors?

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)

Similar Threads