Single Ended Parallel Lead - review my planned overhaul

[Bergheim]

Okay, 90v drop with the 5k and your math checks out! I had right intentions but wrong application!

I see now the error I made - I had put the 4.7k value as a desire to lower preamp voltages, but minor visual error it should go further down the B+ line, not replace the 1k I'm not a huge fan of the funky stock layout, but I have to use what I have ).

I'd like to keep maximum voltage at the power tubes, hence the whole reason of replacing transformer and doubling up on tubes!

Better yet as you suggest, I can omit the B+2 dropper altogether and connect the 5k/5w to the B+ line for max voltage potential, close if not dead on to that 415v figure.

I see now a way I can take that same 4.7k/2w and put it in between B+3 and B+4 filters for preamp voltage dropping. I'll just jumper the 5k/5w over to the immediate right instead of up/down orientation, then simply use new jumper wire to reconnect the B+ line to the preamp.

I'll make an update layout tonight to illustrate that change.

Sounds good regarding the preamp dropping string.
Actually, considering a B+ of 415V and 5k (again, single tube-wise) OT, I think 1/2 B+ voltage of about 200V would be perfect for a screen supply, keeping screen current peaks low when it goes into overdrive. Especially pentodes, that suffer from high screen current, will probably last much longer if screen current is held in check. Too high a screen voltage places the load line far below the knee of the 0V grid curve, and even 290V screens is pushing it a bit, but the 5k dropper ensures that when screen current goes up, voltage will drop a quite lot.

[GlideOn]

AX84 SEL V2.1.pdf

5k/5w dropper rerouted to B+ and 4.7k now after servicing as preamp dropper.

The V2 was now correctly changed proper to 10k dropper as is in original schematic.

If I find the tone too hard/brittle, I'll consider adding an additional 4.7k to 10k in between somewhere, though it looks pretty standard early Fender/Marshall voltages at this point.

Presuming the EL34B is in fact a 30w tube, we faux an equivalent a 30w capable 6L6WGC (I presume it just goes by ballpark wattage per tube) bias it with the 330r on each Cathode @ 71ma and it gives us the following load line:

A beast of a Class A amp.

Screenshot_20240806-180053.png

[Bergheim]

AX84 SEL V2.1.pdf

5k/5w dropper rerouted to B+ and 4.7k now after servicing as preamp dropper.

The V2 was now correctly changed proper to 10k dropper as is in original schematic.

If I find the tone too hard/brittle, I'll consider adding an additional 4.7k to 10k in between somewhere, though it looks pretty standard early Fender/Marshall voltages at this point.

Presuming the EL34B is in fact a 30w tube, we faux an equivalent a 30w capable 6L6WGC (I presume it just goes by ballpark wattage per tube) bias it with the 330r on each Cathode @ 71ma and it gives us the following load line:

A beast of a Class A amp.

Screenshot_20240806-180053.png

If you hover the mouse over the blue input grid lines, you'll find that in the 6L6GC setup, the loadline passes through the knee/bend of the -10V grid line, while the 0V grid line is two lines above that. Assuming the only difference between EL34 and EL34B is the 25W/30W plate dissipation, and plate characteristics are the same, it's perfectly fine to use the normal EL34 for designing purposes. 30W with 415V is 72mA, and we can calculate screen current, voltage drops and bias voltage from there. Screen current is 15% of plate current, so 10.8mA per tube, and bias voltage should be 15.5V if screen voltage is 290V (and just as an example, if screen voltage is 320V, bias voltage has to be 22.3V). So a total cathode current of 72 + 10.8 = 82.8. Bias resistor then has to be 15.5V / 82.8mA = 187R. A 180 will do just fine, And again, actual plate and screen voltage will be their respective supply node voltages minus the bias voltage, so the plate and screen current will be a smidge lower than calculated.

[martin manning]

The Shuguang tube does have indeed have a spec sheet as listed on this site and gives a clear indication listed as a "30w, tube," but hilariously the actual spec of max P is 25w...perhaps they typo'd but it doesn't inspire lots of confidence :lol:

That's for sure. The data sheet also says it's actually a beam tetrode, even though the anode curves are pentode-like. It would be interesting to trace one of these.

[GlideOn]

AX84 SEL V2.1.pdf

5k/5w dropper rerouted to B+ and 4.7k now after servicing as preamp dropper.

The V2 was now correctly changed proper to 10k dropper as is in original schematic.

If I find the tone too hard/brittle, I'll consider adding an additional 4.7k to 10k in between somewhere, though it looks pretty standard early Fender/Marshall voltages at this point.

Presuming the EL34B is in fact a 30w tube, we faux an equivalent a 30w capable 6L6WGC (I presume it just goes by ballpark wattage per tube) bias it with the 330r on each Cathode @ 71ma and it gives us the following load line:

A beast of a Class A amp.

Screenshot_20240806-180053.png

If you hover the mouse over the blue input grid lines, you'll find that in the 6L6GC setup, the loadline passes through the knee/bend of the -10V grid line, while the 0V grid line is two lines above that. Assuming the only difference between EL34 and EL34B is the 25W/30W plate dissipation, and plate characteristics are the same, it's perfectly fine to use the normal EL34 for designing purposes. 30W with 415V is 72mA, and we can calculate screen current, voltage drops and bias voltage from there. Screen current is 15% of plate current, so 10.8mA per tube, and bias voltage should be 15.5V if screen voltage is 290V (and just as an example, if screen voltage is 320V, bias voltage has to be 22.3V). So a total cathode current of 72 + 10.8 = 82.8. Bias resistor then has to be 15.5V / 82.8mA = 187R. A 180 will do just fine, And again, actual plate and screen voltage will be their respective supply node voltages minus the bias voltage, so the plate and screen current will be a smidge lower than calculated.

The thing 6L6GC and EL34B have in common actually is that they are both classified Beam Tetrode.

Also, looking at other EL34L, EL34B, 6L6GC, specifically indicate Beam Tetrode in their descriptions, plus plate voltages of 500v-800v, screen voltages of 450v-500v. Beyond a few grammatical errors and typos, numbers would seem to confirm what we are considering is indeed a 30w which means a smidgen more power and hotter bias.

6L6GC after all is a beefed up version of the 6L6 originally rated for only 19w (and metal casing vs glass for GC). GC is so popular and widely used, that 6L6 is synonymous with 6L6GC. Seems EL34B and EL34L follow the same principle in design, just aren't as popular because the normal EL34 is still very much around.

I'm getting a bit lost however at where the 72ma and 290v screen voltage is now coming from - is the 5k now dropping more voltage being connected directly to the B+ line as shown in latest updated layout?

Or are we still going by the 93v drop from before for a total of 323v screen?

One would have a code too hot, the other slightly cold. So important to know what this Screen V is to get the Cathode R right - again, sperated Cathodes - not shared.

I don't know if it has changed or if it was better practice to stay below the ceiling of the loadline curve.

[Bergheim]

AX84 SEL V2.1.pdf

5k/5w dropper rerouted to B+ and 4.7k now after servicing as preamp dropper.

The V2 was now correctly changed proper to 10k dropper as is in original schematic.

If I find the tone too hard/brittle, I'll consider adding an additional 4.7k to 10k in between somewhere, though it looks pretty standard early Fender/Marshall voltages at this point.

Presuming the EL34B is in fact a 30w tube, we faux an equivalent a 30w capable 6L6WGC (I presume it just goes by ballpark wattage per tube) bias it with the 330r on each Cathode @ 71ma and it gives us the following load line:

A beast of a Class A amp.

Screenshot_20240806-180053.png

If you hover the mouse over the blue input grid lines, you'll find that in the 6L6GC setup, the loadline passes through the knee/bend of the -10V grid line, while the 0V grid line is two lines above that. Assuming the only difference between EL34 and EL34B is the 25W/30W plate dissipation, and plate characteristics are the same, it's perfectly fine to use the normal EL34 for designing purposes. 30W with 415V is 72mA, and we can calculate screen current, voltage drops and bias voltage from there. Screen current is 15% of plate current, so 10.8mA per tube, and bias voltage should be 15.5V if screen voltage is 290V (and just as an example, if screen voltage is 320V, bias voltage has to be 22.3V). So a total cathode current of 72 + 10.8 = 82.8. Bias resistor then has to be 15.5V / 82.8mA = 187R. A 180 will do just fine, And again, actual plate and screen voltage will be their respective supply node voltages minus the bias voltage, so the plate and screen current will be a smidge lower than calculated.

The thing 6L6GC and EL34B have in common actually is that they are both classified Beam Tetrode.

Also, looking at other EL34L, EL34B, 6L6GC, specifically indicate Beam Tetrode in their descriptions, plus plate voltages of 500v-800v, screen voltages of 450v-500v. Beyond a few grammatical errors and typos, numbers would seem to confirm what we are considering is indeed a 30w which means a smidgen more power and hotter bias.

6L6GC after all is a beefed up version of the 6L6 originally rated for only 19w (and metal casing vs glass for GC). GC is so popular and widely used, that 6L6 is synonymous with 6L6GC. Seems EL34B and EL34L follow the same principle in design, just aren't as popular because the normal EL34 is still very much around.

I'm getting a bit lost however at where the 72ma and 290v screen voltage is now coming from - is the 5k now dropping more voltage being connected directly to the B+ line as shown in latest updated layout?

Or are we still going by the 93v drop from before for a total of 323v screen?

One would have a code too hot, the other slightly cold. So important to know what this Screen V is to get the Cathode R right - again, sperated Cathodes - not shared.

I don't know if it has changed or if it was better practice to stay below the ceiling of the loadline curve.

I might stand corrected, but I'm struggling to find EL34B datasheets that have plate characteristics, which would make it much easier to see what they really are. Beam tetrodes have a sharp knee whereas true pentodes have a soft/gradual knee. There also seems to be a debate on the Seymour Duncan forum about wether all brands of the EL34B are beam tetrodes, or if some of the brands are pentodes.
72mA is the current needed to run a 30W tube at 100% dissipation with a plate voltage of 415V. 290V screens was just a ballpark estimate based on a B+1 of 415V minus a bias voltage of 35V, and I now realize that number probably is pretty far out.
If the EL34B is a beam tetrode, screen current is typically only around 5% of the plate current. So with 72mA plate current, screen current is 3.6mA, 7.2mA for both tubes. Voltage drop over the 5k is now 5k * 7.2mA = 36V. If that 5k connects to the 415V point, you'll get a screen node voltage of 379V. To dissipate 100% with this setup, bias voltage has to be -30V. Cathode current will be 72 + 3.6 = 75.6mA. The cathode resistor has to be 30 / 75.6 = 397R. Closest standard value is 390R. If I were you I'd build it like this and see how close actual measurements are to the calculations, and then make neccessary adjustments.

[GlideOn]

Copied from: http://www.analogmetric.com/goods.php?id=24

Shuguang Vacuum Tube EL34 Series

Two tubes for a matched pair
Four tubes for a matched quad

Tetrode: EL34-B


DESCRIPTION

Plate power dissipation of EL34-B can reach 30W, whereas EL34A is 25W. EL34-B belongs to tetrode tube compared to pentode tude of EL34A. g1 and g2 of EL34-B is not exactly aligned opposite to each other and it is used in linear power amplification.


SPECIFICATION

Filament HeatingUH………………6.3V
IH………………..1.5A
Maximum RatingsPlate voltage……………..800V
Second grid voltage…………..500V
First grid voltage……………..-100V
plate power dissipation………….25W
Second grid power dissipation……8W
Cathode current………………….150mA
First grid resistance
For selt-biasing………………..0.7M
For fixed-biasing………………0.5M
Filament voltage between cathode…………100V
Temperature of glass envelop………………250
CapacitancesInput capacitance………………..15.2pF
Output capacitance……………….8.4pF
Muller capacitance……………….1.1pF
First grid-heater capacitance……..1.0pF
Heater filament capacitance……....10pF
DC ParametersUa………………250V
Ug2……………..250V
Ug3………………..0V
-Ug1…………….12.2V
Ia……………….100mA
Gm……………..11mA/V
ri………………..15k
ug1-g2…………..11

[GlideOn]

If you hover the mouse over the blue input grid lines, you'll find that in the 6L6GC setup, the loadline passes through the knee/bend of the -10V grid line, while the 0V grid line is two lines above that. Assuming the only difference between EL34 and EL34B is the 25W/30W plate dissipation, and plate characteristics are the same, it's perfectly fine to use the normal EL34 for designing purposes. 30W with 415V is 72mA, and we can calculate screen current, voltage drops and bias voltage from there. Screen current is 15% of plate current, so 10.8mA per tube, and bias voltage should be 15.5V if screen voltage is 290V (and just as an example, if screen voltage is 320V, bias voltage has to be 22.3V). So a total cathode current of 72 + 10.8 = 82.8. Bias resistor then has to be 15.5V / 82.8mA = 187R. A 180 will do just fine, And again, actual plate and screen voltage will be their respective supply node voltages minus the bias voltage, so the plate and screen current will be a smidge lower than calculated.

The thing 6L6GC and EL34B have in common actually is that they are both classified Beam Tetrode.

Also, looking at other EL34L, EL34B, 6L6GC, specifically indicate Beam Tetrode in their descriptions, plus plate voltages of 500v-800v, screen voltages of 450v-500v. Beyond a few grammatical errors and typos, numbers would seem to confirm what we are considering is indeed a 30w which means a smidgen more power and hotter bias.

6L6GC after all is a beefed up version of the 6L6 originally rated for only 19w (and metal casing vs glass for GC). GC is so popular and widely used, that 6L6 is synonymous with 6L6GC. Seems EL34B and EL34L follow the same principle in design, just aren't as popular because the normal EL34 is still very much around.

I'm getting a bit lost however at where the 72ma and 290v screen voltage is now coming from - is the 5k now dropping more voltage being connected directly to the B+ line as shown in latest updated layout?

Or are we still going by the 93v drop from before for a total of 323v screen?

One would have a code too hot, the other slightly cold. So important to know what this Screen V is to get the Cathode R right - again, sperated Cathodes - not shared.

I don't know if it has changed or if it was better practice to stay below the ceiling of the loadline curve.

I might stand corrected, but I'm struggling to find EL34B datasheets that have plate characteristics, which would make it much easier to see what they really are. Beam tetrodes have a sharp knee whereas true pentodes have a soft/gradual knee. There also seems to be a debate on the Seymour Duncan forum about wether all brands of the EL34B are beam tetrodes, or if some of the brands are pentodes.
72mA is the current needed to run a 30W tube at 100% dissipation with a plate voltage of 415V. 290V screens was just a ballpark estimate based on a B+1 of 415V minus a bias voltage of 35V, and I now realize that number probably is pretty far out.
If the EL34B is a beam tetrode, screen current is typically only around 5% of the plate current. So with 72mA plate current, screen current is 3.6mA, 7.2mA for both tubes. Voltage drop over the 5k is now 5k * 7.2mA = 36V. If that 5k connects to the 415V point, you'll get a screen node voltage of 379V. To dissipate 100% with this setup, bias voltage has to be -30V. Cathode current will be 72 + 3.6 = 75.6mA. The cathode resistor has to be 30 / 75.6 = 397R. Closest standard value is 390R. If I were you I'd build it like this and see how close actual measurements are to the calculations, and then make neccessary adjustments.

Yes, at some point I am just going to have to pick it and be prepared to adjust as-needed. It is still very much a prototype design so nothing is 100% certain from just numbers alone.

I suppose I can have 330r, 390r and 430r values handy.

Install the 390r and take real-world voltages.

Sub any of those as-needed.

Fortune favors the bold!

[martin manning]

This is just the reality we are in. Data sheets show the target characteristics, but there is significant variation in production parts. No one is holding the manufacturers to tight tolerances anymore.

[GlideOn]

This is just the reality we are in. Data sheets show the target characteristics, but there is significant variation in production parts. No one is holding the manufacturers to tight tolerances anymore.

Yep.

I've messaged at least 3 retailers now that carry the Shuguang EL34B and they all more or less say "maybe, but we're not going to bother to confirm as we already have your money due to high demand, so go ahead and knock yourself out buddy."

[GlideOn]

PXL_20240811_022401826.jpg

PXL_20240811_022258391.jpg

PXL_20240811_022410972.jpg

I got the Power Transformer on, more or less. There were absolutely no instructions, no spec sheets included with these things. Helped to use several washer to elevate the mounting bracket, plus a shorter mounting bolt that is in M8 1.5mm threaded metric spacing - not imperial. Curious.

Everything is a super tight fit, but I managed to plumb the wires through safely. There are 2x Red/Black primaries, Brown/Brown and Blue/Blue 6.3v heaters, plus 2x White/Yellow secondaries. I've already messaged AnTek to clarify which does what as there's only old spes sheets with different colored wires, but seems to be the same besides cosmetic color differences.

My biggest concern is that with the cover on, there's a hair's breadth between tubes and transformer. The fat EL34Bs will not fit, only standard 25w EL34s, which I fortunately have.

Supposedly the Torodials run much cooler, plus there's a painted cover between, so maybe this is a non-issue?

I'd prefer to leave the cover on as it looks pretty awesome, covers the windings nearly completely and I can live with having the use regular EL34s.

Will this be a problem?

[TUBEDUDE]

I'd make sure there is room tor a fan. A 12Vdc fan operating at half voltage to keep noise down. There will be some heat to remove from that chassis.

[Bergheim]

I'd remove the PT cover. It'll help air ventilation around the PT and tubes, and maybe you'll be able to fit bigger bottles as well. All the unconvenience seems like a big price to pay compared to somewhat better aesthetics (that people will have to cramp their heads behind the amp to appreciate anyways). IMHO

[GlideOn]

I'd make sure there is room tor a fan. A 12Vdc fan operating at half voltage to keep noise down. There will be some heat to remove from that chassis.

I agree.

I thought about this too, perhaps not on/in the amp itself but externally on the chassis as there's a bit of room rear of the amp.

PXL_20240811_135917697.MP.jpg

PXL_20240811_135900655.MP.jpg

I was thinking this standalone 2x 120mm fans with a standard 110v plug to keep outside of the amp, maybe use an adapter off the IEC amp socket:

ANEXT, 120mm AC Computer Fan Black, 120mm*240mm, Silent Fan for Receiver DVR PlayStation Xbox Computer Cabinet Cooling https://a.co/d/0eFMiNW

Toptekits C14 to C13+NEMA 5-15R Y Splitter Power Plug Cord,Single IEC 320 C14 Male to C13+Nema 5-15R Female Splitter Adapter Cable Cord(C14 to C13/5-15R 1ft) https://a.co/d/8vcViFA

I'd remove the PT cover. It'll help air ventilation around the PT and tubes, and maybe you'll be able to fit bigger bottles as well. All the unconvenience seems like a big price to pay compared to somewhat better aesthetics (that people will have to cramp their heads behind the amp to appreciate anyways). IMHO

It's kind of uncharted territory here as there's zero information of expected heat generation from AnTek. It is made from steel, has about 1/8in inside air gap, shields against RF, protects the bare wires a fare bit but not integral to the operation of it. I don't think the transformer and by extension the cover will produce much perceivable heat. It very well may be cool to the touch in practice and the only real concern would be the radiating heat of the power tubes progressively warming up the cover. A fan setup would certainly mitigate a lot of the radiating/warming effect of the cover.

The only real-world situation I can think of being an open-back combo would be for some object to pierce through the transformers by it falling backwards somehow. In that case, a mesh cage on the upper half would do an equal job of protecting the PT and entire amp at that.

It is removable; may try with the cover on for now, take some readings with heat gun or borrow thermal camera from my AC tech friend, then see how we fare.

[cdemike]

I'd make sure there is room tor a fan. A 12Vdc fan operating at half voltage to keep noise down. There will be some heat to remove from that chassis.

I agree.

I thought about this too, perhaps not on/in the amp itself but externally on the chassis as there's a bit of room rear of the amp.

PXL_20240811_135917697.MP.jpg

PXL_20240811_135900655.MP.jpg

I was thinking this standalone 2x 120mm fans with a standard 110v plug to keep outside of the amp, maybe use an adapter off the IEC amp socket:

ANEXT, 120mm AC Computer Fan Black, 120mm*240mm, Silent Fan for Receiver DVR PlayStation Xbox Computer Cabinet Cooling https://a.co/d/0eFMiNW

Toptekits C14 to C13+NEMA 5-15R Y Splitter Power Plug Cord,Single IEC 320 C14 Male to C13+Nema 5-15R Female Splitter Adapter Cable Cord(C14 to C13/5-15R 1ft) https://a.co/d/8vcViFA

I'd remove the PT cover. It'll help air ventilation around the PT and tubes, and maybe you'll be able to fit bigger bottles as well. All the unconvenience seems like a big price to pay compared to somewhat better aesthetics (that people will have to cramp their heads behind the amp to appreciate anyways). IMHO

It's kind of uncharted territory here as there's zero information of expected heat generation from AnTek. It is made from steel, has about 1/8in inside air gap, shields against RF, protects the bare wires a fare bit but not integral to the operation of it. I don't think the transformer and by extension the cover will produce much perceivable heat. It very well may be cool to the touch in practice and the only real concern would be the radiating heat of the power tubes progressively warming up the cover. A fan setup would certainly mitigate a lot of the radiating/warming effect of the cover.

The only real-world situation I can think of being an open-back combo would be for some object to pierce through the transformers by it falling backwards somehow. In that case, a mesh cage on the upper half would do an equal job of protecting the PT and entire amp at that.

It is removable; may try with the cover on for now, take some readings with heat gun or borrow thermal camera from my AC tech friend, then see how we fare.

The only amp I built with an Antek PT runs pretty cool, but it's a very different setup so YMMV. The big tradeoff I am aware of between toroidal and EI transformers other than inrush current is magnetic flux. Antek's covers being ferrous may prove helpful in terms of preventing unwanted interaction between the transformer and your output tubes.