SE versus PP

[benito_red]

hello to everybody,
I recently discovered this interesting forum, and I would like to ask a question about what differences there are between a SingleEnded and a PushPull amp. Of course the first difference is the amount of the power, but beside that, what difference about tone?
Let's talk for istance about two different Fender: the AA764 (Champ BF) and the AA964 (Princeton BF), the second seems to be the PP version of the first. Only one difference in the tone stack: the 15k resistor in the Champ vs the 6,8k in the Princeton.
If they would be connected to the same speaker/cabinet, how would they sound?
Thanks a lot
benito

[MWJB]

Firstly there are other relevant differences...you're not really comparing like with like.

You have noted already that the Princeton has a 6.8K mid resistor value, whereas the Champ has 15K...these values could be swapped, or both amps could be fitted with a 25K mid pot to allow the mids to be adjusted to taste. Champ probably has 15K to give it a more "forward" sound, given the limitations of speaker & design.

The Princeton, as well as being PP, is also fixed bias - this gives a tighter sound, better headroom & perhaps slightly less interesting harmonic content than cathode bias (Champ). Cathode bias tends to have a more emphasised envelope of attack & decay, runs the tubes at less voltage (sounds browner, less power) and has richer harmonic content. Again, either amp could be converted to fixed or cathode bias, or fitted with a DPDT switch to allow operation in either mode.

Being PP, The Princeton requires an additional tube, the phase inverter, to split the signal between the 2 power tubes. This is less relevant to the Princeton (non-reverb) as this is "missing" a tone stack recovery stage and is low on gain for a Fender. The Princeton Reverb subsequently has much more gain (even discounting anything added by the reverb).

If all things were equal (mid resistor, method of bias, preamp stages) the SE amp would sound crunchier & fuzzier when overdriven. The PP amp would be cleaner smoother and make around 3 times the power.

Champ through a 10" will still sound like a champ (assuming output impedances are matched in all cases), just with a little more headroom & better projection (assuming a reasonably similar style speaker). Princeton through the champ's 8" would probably not be a good idea in the long run due to the power difference, but a typical 8" guitar speaker would cut headroom/fidelity, but may sound warmer.

[imaradiostar]

I think the phase inverter plays a part too- the Princeton in stock configuration gets asymmetrical when driven hard. This can have a big effect on the tone though the negative feedback takes care of a lot of it.

jamie

[benito_red]

hello MWJB and Imaradiostar,
thanks a lot for your answers.
MWJB wrote:
"... If all things were equal (mid resistor, method of bias, preamp stages) the SE amp would sound crunchier & fuzzier when overdriven. The PP amp would be cleaner smoother and make around 3 times the power. ..."

but what about the clean sound? I suppose that perhaps even below the clipping the SE performs more trebly and thinner, however it should retain his Fender "imprinting".
What do you think about?
bye benito

[MWJB]

The SE won't necessarily sound more trebly & thinner...in fact if I was recording, I'd go for the champ every time, as the tighter, cleaner PP amp will normally sound thinner when recorded. Yes, the Champ will still sound like a Fender.

Other than a very controlled environment, you're not likely to play a Champ "below clipping". So the Princeton will still hold up for small club gigs with a sympathetic band behind it, the champ won't unless mic'd up.

That's the heart of the matter...people choose amps for the volume levels they have to work with. Small practice amps are made to be cheap, so SE makes sense to keep parts count low & final product cheap. If you want more than 10W you go PP.

[Old Tele man]

Champ is SE Class-A (lowest distortion, predominately even harmonics); has air-gap OT to control core saturation; B+ about 350Vdc; 1 x 6V6GT = about 2-3W power output.

Princeton is PP Class-AB1 (higher power, predominately odd harmonics); has split primary OT to cancel power tube induced even harmonics; B+ about 420Vdc; 2 x 6V6GT = about 10-12W power output.

[MWJB]

"Champ is SE Class-A (lowest distortion, predominately even harmonics); has air-gap OT to control core saturation; 1 x 6V6GT = about 3W power output" True enough, but very few players will play a Champ at RMS rated output...so a crunchy 6W is more typical.

Princetons can push 20W under normal gigging circumstances.

[Bruce / Mission Amps]

Originally Posted by Old Tele man

Champ is SE Class-A (lowest distortion, predominately even harmonics); has air-gap OT to control core saturation; B+ about 350Vdc; 1 x 6V6GT = about 2-3W power output. ...

Thank you for that.. it drives me crazy when sometime keeps calling these cheap class A Champs with a postage stamp sized OT a 5 or 6 watt amp.
I've never had or seen one that could make more then 2 or 3 "clean/linear" watts into a dummy load at any reasonable low freq and drive level.
Many come in here and can't even muster 1.5 to 1.75 clean watts to be honest.

[HTH]

I've got into SE amps in a big way over the past year or so - one day I'd love to build a SE amp in the 30w range so I could have a SE amp loud enough to gig.

It'd be one beast of an amp in terms of weight, but I bet the tone would be sweet.

[MWJB]

Many of us have/had the same fantasy...in reality though you'd end up with an amp that weighed as much as a Super Reverb, maybe a Twin, but would only keep up with a PV C30! For the cost & effort a PP amp always seems to win out as the sensible option, there are things you can do to increase even order harmonics, to give a more SE vibe, or even try running one KT88/90 in a 2x6L6 PP amp & run hotter plate current (not so hot as to burn the OT of course & you still won't get 30 RMS). You won't have the air gapped SE OT if you try this, but even a 30W SE guitar amp isn't going to run clean at typical gig volume.

[mooreamps]

A couple years ago I built a couple 36 watt SE amps using a KT88 and an EL34 running a plate voltages switchable between 300 volts and 600 volts. I though it was pretty loud enough...

[Old Tele man]

Originally Posted by mooreamps

A couple years ago I built a couple 36 watt SE amps using a KT88 and an EL34 running a plate voltages switchable between 300 volts and 600 volts. I though it was pretty loud enough...

...in one of my engineering textbooks is a statement I've always remembered: '...only 15W is needed for the average size room...' said of Hi-Fi stereo system. Of course, the text didn't clarify whether that was TOTAL power or per channel, ha,ha!

[HTH]

Originally Posted by mooreamps

A couple years ago I built a couple 36 watt SE amps using a KT88 and an EL34 running a plate voltages switchable between 300 volts and 600 volts. I though it was pretty loud enough...

nice one, glad that someone else is as crazy as me in even considering such an amp

I'm envisaging a 4x EL34 SE head which will hopefully put out around 40w-50w with the plates around 400v.

Am I right in thinking that each EL34 will pull around 80mA at that kind of voltage and I'd therefore need a PT with a HT winding capable of handling at leas 320mA. Of course the OT would also need to be able to handle at least 320mA too.

Trouble is, where do I get a 300-0-300 PT with a 320mA (or more) HT winding and also an OT to match ??? - am I in the territory of having to parallel the transformers up?

[mooreamps]

Well, at 400 volts you don't want the plate dissipation on an EL-34 too much more than about 12 watts. Therefore, you will want to keep the plate current in the 30 mil range.


-g

[MWJB]

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?

[mooreamps]

Originally Posted by MWJB

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]

Originally Posted by mooreamps

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...

YouTube- HTH AMPLIFICATION, 10w class A EL34 combo

YouTube- HTH AMPLIFICATION, 10w class A EL34 combo

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]

Originally Posted by MWJB

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]

Originally Posted by 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.

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]

Originally Posted by mooreamps

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]

Originally Posted by 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

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]

Originally Posted by Chuck H

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

[mooreamps]

I still have a half baked 813 project still sitting in my lab. The power transformer is big, but now as big as this one. I'm still pondering on the layout for the preamp and the PI I want to use to finish it up.

-g

[Old Tele man]

Originally Posted by mooreamps

I still have a half baked 813 project still sitting in my lab. The power transformer is big, but now as big as this one. I'm still pondering on the layout for the preamp and the PI I want to use to finish it up.

-g

...the "mega"-Champ at 1 kilowatt of power, for the really B-I-G bedroom venue (ha,ha)!

[Steve Conner]

This is the biggest SE amp I've seen:
The 304TL Amplifier

John Chambers' 1kW amp is certainly impressive, but it's push-pull Class-AB, so it doesn't count. If it were running single ended, he'd only be getting about 100W out of those same tubes.

HTH: Your 10 watt combo sounds great. What guitar are you using to demo it?

[mooreamps]

Originally Posted by Steve Conner

This is the biggest SE amp I've seen:
The 304TL Amplifier

John Chambers' 1kW amp is certainly impressive, but it's push-pull Class-AB, so it doesn't count. If it were running single ended, he'd only be getting about 100W out of those same tubes.

HTH: Your 10 watt combo sounds great. What guitar are you using to demo it?

Again, you're writing comments on things you don't understand. The max plate dissipation of an RCA-813 tube is 125 watts. Further, it only requires 5 amps filament current verses the 25 amp requirement for the 304TL. I think with 4 813's in parallel he'd get a few more than 100 watts out of it.


-g

[Steve Conner]

I don't think you understand any better. You once mentioned you were going to try and build an 813 amp with a 100 watt Hammond OT or something.

A 304TL can dissipate 300W, and the Alum Rock guy only gets 30W out of one single-ended, so I stand by my 100W claim unless someone can supply hard evidence to the contrary.