Jor-EL34 SE Amp Project

[Curious_George]

On 8/26/2022 at 5:36 PM, Curious_George said:

 

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[captainbeefheart]

I did make a mistake, I was mucking around with it and saw I used a 12AY7 instead of a 12AV7, they are similar but not the same. Will retest with the correct driver tube.

 

Sorry about that.

 

When building no feedback amps it's paramount to select the most linear tubes, the EL34 is in my opinion a much better tube triode strapped compared to the 6L6 types. I never liked the 6L6 types even with feedback so I just stopped using them a long while back.

 

I like your circuit with the EL34 and have made similar no feedback amps. It's probably the most popular topology for single ended amps coming from China but you see 6N1 (similar to 6DJ8) or 6N3 (similar to 5670/2C51) as the front end stage tube. That and the other very popular driver arrangement is just placing the two triodes in parallel, those are often a 6SL7 but also have seen them use 6N1 or 6N3. The output stage is usually wired UL with triode switch.

 

I like the style driver you used (half mu follower?) the best from all the China amp versions , they sounded better than the versions that came with the triodes in parallel. All sounded best to me in triode mode.

 

A couple friends of mine were real heavy into these Chinese amps and I helped them modify them into all kinds of different circuits over the years. I think the two of them bought 10 of them between the two of them. That's how I got to finding out the output transformers aren't really all that bad that come with those amps, we got some really good results with them.

 

 

[Curious_George]

3 hours ago, tube fanatic said:

Nick, can you post your load line drawn on the triode plate curves?  I can’t imagine getting more than a couple of watts from a 6L6 at the operating point you specified, and would venture that the distortion would be upwards of 8%.  Thanks…

 

Maynard

I did not plot a load line for the 6L6. I figured I would just plug one in and see how it biased up. The Chinese OPT in the amp calculated out as 3.8k, but it was probably designed to be 3.5k.

[captainbeefheart]

Wow I just had a look and those kits they were buying went way up in price!! They were $250 then another $100 shipping. Now it's $429 plus $100 shipping. I was almost going to recommend people get the kit and wire it to your circuit but I don't know if it's a great deal anymore. One will have to crunch what it costs for parts and compare.

 

https://www.ebay.com/itm/251514808784?epid=20010103033&hash=item3a8f7369d0:g:hfcAAOSwX0BhXrej&amdata=enc%3AAQAHAAAA8G1nkR4qErKbT%2BsB1RSRpmn2XSyK0DM8wjFv9kB6BQ6mnJ4V0q0dvjvUAaNWTYOMO8RxyKhdNfock%2BJwKPXYJsyhK5DJyT7XpnRiK293pQaTJIt9r9IYbqP%2FkT2HEfccvzJ7mRibzBfegQ569VcHwVfq%2B6B1Np8%2B4YVaHdBe5aGbjqPiR0QtH92mtoAVKVuq0phxbVW47rlzcXT%2F8XyanPwleSFfXmJ9svsRM1XhTt%2FmvgZ0pUEIp%2Bqezcjio0UoaN%2FSt4R05HhbSWNHkNSq4yPBRhYXKdVzHQazxklMxlHglfL2yXJMPsc8UmHc6PB5KQ%3D%3D|tkp%3ABk9SR6DLyMbbYA

[Curious_George]

19 minutes ago, captainbeefheart said:

Wow I just had a look and those kits they were buying went way up in price!! They were $250 then another $100 shipping. Now it's $429 plus $100 shipping. I was almost going to recommend people get the kit and wire it to your circuit but I don't know if it's a great deal anymore. One will have to crunch what it costs for parts and compare.

 

https://www.ebay.com/itm/251514808784?epid=20010103033&hash=item3a8f7369d0:g:hfcAAOSwX0BhXrej&amdata=enc%3AAQAHAAAA8G1nkR4qErKbT%2BsB1RSRpmn2XSyK0DM8wjFv9kB6BQ6mnJ4V0q0dvjvUAaNWTYOMO8RxyKhdNfock%2BJwKPXYJsyhK5DJyT7XpnRiK293pQaTJIt9r9IYbqP%2FkT2HEfccvzJ7mRibzBfegQ569VcHwVfq%2B6B1Np8%2B4YVaHdBe5aGbjqPiR0QtH92mtoAVKVuq0phxbVW47rlzcXT%2F8XyanPwleSFfXmJ9svsRM1XhTt%2FmvgZ0pUEIp%2Bqezcjio0UoaN%2FSt4R05HhbSWNHkNSq4yPBRhYXKdVzHQazxklMxlHglfL2yXJMPsc8UmHc6PB5KQ%3D%3D|tkp%3ABk9SR6DLyMbbYA

It could still be a “deal” if one wanted to do minimal chassis work. $550 for a nice EL34 amp is not bad. 

[Curious_George]

https://www.ebay.com/itm/133632180413?hash=item1f1d1940bd:g:4NQAAOSwfSFhwp0o&amdata=enc%3AAQAHAAAA4CO52824qSrpF%2BJiz5BSwO2sD4d%2FnsKBCB%2BBaD2O0Oq3O66njSr044tLaqohnfWzQvYVDxGPRC2qF4nzO%2BWTjRLze0SvemBsRagtJHkU0H3SvmPWWsgQ%2F6gTb0IeA6CrM7b72r0ucEhK74JamEgFJ%2B1csvj3uFnRS%2BpKlDbYXcPSxN5XFmBccCe9prtXpw6kmW%2FQRuXgwMT0EXfo%2F1EGI2yIkMV2GG1%2ByXxCBGOmj7BUJJoXYPboOSu4fav%2Fe95xRHcqoYcQDnvtI1YNVd8WG5LWSaMlDSKocmhCRz0JyY3o|tkp%3ABFBMyMSgyNtg
 

This one may be the one to get. $350 including shipping.

[Racer X]

Thanks Curious George, I was eyeing that very EL34 SE amp for $350, then I found some 20W OTL amps.  But I still have interest in this amp....

[Curious_George]

7 minutes ago, Racer X said:

Thanks Curious George, I was eyeing that very EL34 SE amp for $350, then I found some 20W OTL amps.  But I still have interest in this amp....

What’s better is that it ships from LA. 

[captainbeefheart]

36 minutes ago, Curious_George said:

https://www.ebay.com/itm/133632180413?hash=item1f1d1940bd:g:4NQAAOSwfSFhwp0o&amdata=enc%3AAQAHAAAA4CO52824qSrpF%2BJiz5BSwO2sD4d%2FnsKBCB%2BBaD2O0Oq3O66njSr044tLaqohnfWzQvYVDxGPRC2qF4nzO%2BWTjRLze0SvemBsRagtJHkU0H3SvmPWWsgQ%2F6gTb0IeA6CrM7b72r0ucEhK74JamEgFJ%2B1csvj3uFnRS%2BpKlDbYXcPSxN5XFmBccCe9prtXpw6kmW%2FQRuXgwMT0EXfo%2F1EGI2yIkMV2GG1%2ByXxCBGOmj7BUJJoXYPboOSu4fav%2Fe95xRHcqoYcQDnvtI1YNVd8WG5LWSaMlDSKocmhCRz0JyY3o|tkp%3ABFBMyMSgyNtg
 

This one may be the one to get. $350 including shipping.

 

Yes much better price but I wonder about the output transformers. The other one had grain oriented silicon steel transformers. If the output transformers are identical then yes it's a much better deal.

 

Have to do some more digging.

[captainbeefheart]

The power transformer looks much larger on the more expensive version. The outputs are potted so hard to compare them by looks.

 

The difference in price is probably due to more expensive output transformers.

[Curious_George]

1 hour ago, captainbeefheart said:

The power transformer looks much larger on the more expensive version. The outputs are potted so hard to compare them by looks.

 

The difference in price is probably due to more expensive output transformers.

The one for $350 indicated the OPT's used Z11, which I believe is Hi-B orient core. So those cores would/could be smaller compared to M6.

[captainbeefheart]

1 hour ago, Curious_George said:

3 hours ago, captainbeefheart said:

 

The one for $350 indicated the OPT's used Z11, which I believe is Hi-B orient core. So those cores would/could be smaller compared to M6.

 

The output transformers for both amps say "Japan Z11" which is why I was wondering if they are the same, just one potted in the more expensive one.

 

The power transformer for the more expensive one has stated it's 96-60 large iron core, 200 watt rated power and .35mm high flux grain oriented silicon sheets (goss) and looks to be larger than the other amp. The $350 one doesn't say anything special about the power transformer. Curious if the power transformer runs cooler on the more expensive one, as I remembered they ran hot on the kits I have experience with so maybe they beefed them up and that's the increase in cost?

[captainbeefheart]

For those that don't know Z11 steel tends to be the darker laminates compared to M6 and has higher permeability. Like for like core and bobbin/winding the Z11 will give greater inductance.

 

Nick and I both have had great experiences with these transformers that come with these cheap Chinese kits. I think they are pretty high quality for what you pay for them which also includes everything for the amp.

[Racer X]

Still feeling my way around the various output transformers, which seem to be the most critical part in any transformer coupled amp.  My Fisher 500C had very hefty output transformers to support 30 wpc.  Should output transformers be larger ?  Smaller may be better ?  Goldilocks ?

Do smaller OPTs favor the high end and run warmer ?

[captainbeefheart]

10 minutes ago, Racer X said:

Still feeling my way around the various output transformers, which seem to be the most critical part in any transformer coupled amp.  My Fisher 500C had very hefty output transformers to support 30 wpc.  Should output transformers be larger ?  Smaller may be better ?  Goldilocks ?

Do smaller OPTs favor the high end and run warmer ?

 

Doesn't matter how they are built, the goal is to get high inductance with low leakage inductance and low inter-winding capacitance. The former gives low distortion at low frequencies and the latter gives greater high frequency extension. There is always a resonance and that should be well above the audio frequency spectrum.

 

There is no free lunch and to get one typically is a trade-off with the other, you need to find a balance. There are also many different techniques and materials. It's a mixture of science and black art, good luck getting winders to tell you their tricks and secrets.

[captainbeefheart]

One example of transformer design is the McIntosh OPT.

 

In a normal output circuit, using 6L6's in push-pull, the tube load impedance is 4000 ohms. A transformer is needed to match the typical speaker impedance of 8 ohms. This represents an impedance ratio of 500 to 1. The necessary transformer turns ratio is the square root of 500, or 22 to 1. Leakage inductance and shunt capacitance cause high frequency rolloff. It also causes notch distortion in class B operation.

The Unity Coupled transformer distributes the load to the output tubes plate and cathode instead of just the plate and effectively reduces the impedance to 1000 ohms. The impedance ratio is lowered to 125 to 1. The turns ratio is reduced to the square root of 125, or 11 to 1. Leakage inductance and shunt capacitance are greatly reduced. By using the bifilar winding technique, leakage inductance is eliminated between primary sections.

 

For the Mcintosh circuit since there is not the normal gain in the output stage from the split loading scheme the front end needs tons of gain. But still because of the design of the output transformer and circuit, the McIntosh amplifiers have very high bandwidth which is unusual in tube amps utilizing an output transformer.

[Curious_George]

15 hours ago, captainbeefheart said:

The power transformer looks much larger on the more expensive version. The outputs are potted so hard to compare them by looks.

 

The difference in price is probably due to more expensive output transformers.

Just because the OPT's look potted, don't mean they are potted. On four of the five Chinese amps I have bought, only one had "true" potted OPT's. The other ones only had cosmetic covers. The Chinese military hardware is the same way...

[Curious_George]

13 hours ago, captainbeefheart said:

 

Doesn't matter how they are built, the goal is to get high inductance with low leakage inductance and low inter-winding capacitance. The former gives low distortion at low frequencies and the latter gives greater high frequency extension. There is always a resonance and that should be well above the audio frequency spectrum.

 

There is no free lunch and to get one typically is a trade-off with the other, you need to find a balance. There are also many different techniques and materials. It's a mixture of science and black art, good luck getting winders to tell you their tricks and secrets.

RF & audio transformer winding; black art, luck and empirical experience, no doubt.

[Curious_George]

.

[captainbeefheart]

55 minutes ago, Curious_George said:

ust because the OPT's look potted, don't mean they are potted. On four of the five Chinese amps I have bought, only one had "true" potted OPT's. The other ones only had cosmetic covers. The Chinese military hardware is the same way...

 

I agree, I am thinking the output transformers are actually the same, just one is covered.

 

The power transformers look much different, and the description of the more expensive one is probably from complaints the original transformers ran hot so they offered up kits with larger versions hence the description of the beefed up power transformer. Not sure it's worth the extra $75 though.