SE versus PP

[mooreamps]

50-60mA would be more typical for a EL-34 at 400vdc on the plate, IF cathode biased. Fixed bias, anything up to 50mA might work? Really though, for the power you are thinking about, more plate volts would be a good idea (adjust current accordingly), as would fixed bias.

Parallelling 4 tubes sounds quite ambitious?

You are actually more correct. I don't know where I saw 12 watts from. Max plate disipation for an EL-34 is 25 watts. Thereby, at 400 volts max plate current would in the range of 62.5 millamperes. So if he ran at 50 mills, he is looking at a power transformer to supply 200 mills for 4 power tubes, plus lets say another 50 for the preamp. So, this Hammond power transformer would work :

372JX 243VA, 300-0-300 @ DC ma 250, 5VCT @ 4A, 6.3VCT @ 8A.


Filament current for 4 EL-34's is : 4 * 1.6 = 6.4 amperes. This leaves 1.6 amperes for preamp filaments. This should leave plenty of margin on the filament supply, and have an option if he wants to use a tube rectifier.


The largest SE output transformer I see is the Hammond 125GSE Single Ended Output Transformer. 25 audio watts, max. D.C. bias 100mA. So, ya maybe you would need two of these. It wieghs about 6 pounds so judge your layout accordingly.





-g

[Sir Cuitous]

It's not just the weight of the SE OT, it's the size. They get big FAST as the power rating increases. I'm not surprised that the Hammond line tops out at 25watts. I built a 2x6V6 SE amp using the Hammond 125ESE OT. It was too big to place on the same side of the chassis/speaker as the PT. It's a little bigger than the PT that I used and I imagine that the higher powered SE OTs just get bigger from there. I believe the size issue (and therefore "price") is why we don't see more higher powered SE amps. BTW I really like the tone of the Hammond SE OTs, but I would guess that I am only getting about 6 - 7 watts out of two 6V6s SE.

[HTH]

You are actually more correct. I don't know where I saw 12 watts from. Max plate disipation for an EL-34 is 25 watts. Thereby, at 400 volts max plate current would in the range of 62.5 millamperes. So if he ran at 50 mills, he is looking at a power transformer to supply 200 mills for 4 power tubes, plus lets say another 50 for the preamp. So, this Hammond power transformer would work :

372JX 243VA, 300-0-300 @ DC ma 250, 5VCT @ 4A, 6.3VCT @ 8A.


Filament current for 4 EL-34's is : 4 * 1.6 = 6.4 amperes. This leaves 1.6 amperes for preamp filaments. This should leave plenty of margin on the filament supply, and have an option if he wants to use a tube rectifier.


The largest SE output transformer I see is the Hammond 125GSE Single Ended Output Transformer. 25 audio watts, max. D.C. bias 100mA. So, ya maybe you would need two of these. It wieghs about 6 pounds so judge your layout accordingly.

-g

looking at the notes from my last SE EL34 build, it ended up with the OP valve drawing 69mA...

* cathode resistor= 330ohm
* plate= 372v
* cathode= 23v

... so I was a little bit off thinking they would pull 80mA each at 400v, more like 60mA a piece which is still a 240mA HT winding and OT.

I saw the Hammond 372JX too, but didn't consider it when I thought I'd be looking at a 320mA HT winding. That's be one beast of a PT - it's around the same size as the 370HX I used on my previous SE EL34 build.

As for an OT, I've used the 125GSE too and its a great sounding OT... [ame="http://www.youtube.com/watch?v=Ut38iY4-h7o"]YouTube- HTH AMPLIFICATION, 10w class A EL34 combo[/ame]

Hammond have a 1600SE series that has OTs with much higher current ratings, but they have fixed primaries unless you run them with an unmatched speaker load to reflect the desired primary Z.

With my previous SE EL34 amp I ran it at 5k, with each additional EL34 in parallel, do we double the primary Z like with a PP amp ????

with two EL34s in parallel, I'd want a ???k primary
with three EL34s in parallel, I'd want a ???k primary
with four EL34s in parallel, I'd want a ???k primary

Many Thanks to help for all, Ian

[MWJB]

2xEL34 in parallel = 1.8K to 2K
3xEL34 in parallel = 1K to 1.5K
4xEL34 in parallel = are you really sure you want to do this, why not use more powerful tubes 6550/KT88, but less of them? You're going to have overly long grid wires, how will all the tubes get decent signal from the preamp, miller effect?, 3 tubes in parallel is probably pushing it.

[Old Tele man]

You're going to have overly long grid wires, how will all the tubes get decent signal from the preamp, miller effect?, 3 tubes in parallel is probably pushing it.

...with SE, all the tubes COULD be placed in a common circular pattern to produce a minimum tube-to-tube distance. Some of the "old" cyclotron(sp?) amp configurations were wired this way.

[HTH]

2xEL34 in parallel = 1.8K to 2K
3xEL34 in parallel = 1K to 1.5K
4xEL34 in parallel = are you really sure you want to do this, why not use more powerful tubes 6550/KT88, but less of them? You're going to have overly long grid wires, how will all the tubes get decent signal from the preamp, miller effect?, 3 tubes in parallel is probably pushing it.

I know it's not the most sane amp build anyone will ever embark on, but I've played with various valve types in SE amps and like EL34s best (actually, I like EL34s best PP too).

A pair of 6550s wired parallel SE would be more practical for a 40w SE amp, but its all about the tone and the buzz from building something a little different

Oh, and thanks for the help too - always appreciated

[mooreamps]

Who said any of us claimed to be sane ??


-g

[Old Tele man]

...isn't sanity an 'hors d'oeuvre' that's best served with lunacy...or Farber beans?

[HTH]

Who said any of us claimed to be sane ??


-g

I'm in with the right crowd then. Ok, I'm off to drink my own piss and write my journal in my own shite

[benito_red]

"With my previous SE EL34 amp I ran it at 5k, with each additional EL34 in parallel, do we double the primary Z like with a PP amp ????

with two EL34s in parallel, I'd want a ???k primary
with three EL34s in parallel, I'd want a ???k primary
with four EL34s in parallel, I'd want a ???k primary"

the theory states that if you load a single SE tube, in this case one EL34 with 5K-Ohm, if you want to double the output power at the same working point you must put in parallel two EL34 and the primary load will be in this case 5K/2 = 2,5K-Ohm. with 3xEL34 in parallel it will be 5K/3 and so on.
The same calculation is valid for PP, in fact the Vox AC15 had 2 x EL84 with 8K-Ohm anode-to-anode releasing 15Watt. The Vox AC30 had 4 x EL84 with 4K-Ohm anode-to-anode releasing 30Watt but at the same working point of the AC15.
Working point = bias and load condition

regards
benito

PS sorry but for some reason i did not see that it was already answered that tthe question

[HTH]

"With my previous SE EL34 amp I ran it at 5k, with each additional EL34 in parallel, do we double the primary Z like with a PP amp ????

with two EL34s in parallel, I'd want a ???k primary
with three EL34s in parallel, I'd want a ???k primary
with four EL34s in parallel, I'd want a ???k primary"

the theory states that if you load a single SE tube, in this case one EL34 with 5K-Ohm, if you want to double the output power at the same working point you must put in parallel two EL34 and the primary load will be in this case 5K/2 = 2,5K-Ohm. with 3xEL34 in parallel it will be 5K/3 and so on.
The same calculation is valid for PP, in fact the Vox AC15 had 2 x EL84 with 8K-Ohm anode-to-anode releasing 15Watt. The Vox AC30 had 4 x EL84 with 4K-Ohm anode-to-anode releasing 30Watt but at the same working point of the AC15.
Working point = bias and load condition

regards
benito

PS sorry but for some reason i did not see that it was already answered that tthe question

thanks for that Benito, much appreciated.

[BackwardsBoB]

Wow. That amp sounds like rock!

[Chuck H]

I once thought of building a class A amp with a single giant transmitter tube for the output. I've never even tried to source the parts for this. It's just a fantasy really. I'd of course have to design it so the one giant tube stuck straight up out of the amp in a circular wire cage. Oh, and one of those lever style Dr. Frankenstien lab switches that you have to grab in your fist and a big round face panel meter with old yellowed glass on the front... Cool.

Chuck

[mooreamps]

I once thought of building a class A amp with a single giant transmitter tube for the output.

Chuck

You mean one like this one ?? I think an amp like that would be like Mount Bichen !!


http://www.chambonino.com/construct/const9.html


-g

[Chuck H]

...Wow

Those transformers are like bowling balls. Even Ken Gilbert (owner/creator of the notorious BAGA) would be impressed.

Chuck