Wanting to Build an EL84 Amp, but which one?

[macaltec]

I have been reading and studying the RH84 amp. I have a good grasp on the BOM and felt like I was ready to start ordering materials. Then I saw the new sticky about Kegger schematics and the SEUL EL84 w/6BK7.

So let me start with the following:
1) I chose an EL84 amp because I have 4 very nice Amperex Bugle Boy 7189's that I hope to use. Can I use them as a direct substitute for the the EL84
2) I am asking the collective knowledge here to help me understand some of the pros and cons of each design.
3) Could I use the same power supply design, CLC, from the RH84 on the SEUL EL 84, obviously tweaking it to get the proper B+?
4) It appears to me that I could use the same PS and OP (10W-5K) transformers for either design. Am I correct or am I all wet?

That should be enough information for me to digest for now. Thanks for any and all help.

 

[FlaCharlie]

I have been reading and studying the RH84 amp. I have a good grasp on the BOM and felt like I was ready to start ordering materials. Then I saw the new sticky about Kegger schematics and the SEUL EL84 w/6BK7.

So let me start with the following:
1) I chose an EL84 amp because I have 4 very nice Amperex Bugle Boy 7189's that I hope to use. Can I use them as a direct substitute for the the EL84
2) I am asking the collective knowledge here to help me understand some of the pros and cons of each design.
3) Could I use the same power supply design, CLC, from the RH84 on the SEUL EL 84, obviously tweaking it to get the proper B+?
4) It appears to me that I could use the same PS and OP (10W-5K) transformers for either design. Am I correct or am I all wet?

That should be enough information for me to digest for now. Thanks for any and all help.

I can't help you with the pros and cons of each design but I think you're good on all the other questions. I'm sure there are many other designs that might also merit consideration.

 

[kward]

1) I chose an EL84 amp because I have 4 very nice Amperex Bugle Boy 7189's that I hope to use. Can I use them as a direct substitute for the the EL84
2) I am asking the collective knowledge here to help me understand some of the pros and cons of each design.
3) Could I use the same power supply design, CLC, from the RH84 on the SEUL EL 84, obviously tweaking it to get the proper B+?
4) It appears to me that I could use the same PS and OP (10W-5K) transformers for either design. Am I correct or am I all wet?

1. Yes, but you cannot substitute in reverse, in other words a plain old EL84 is not a proper substitute for a circuit that calls for a 7189.
2. They are similar designs. Results obtained I expect will be similar.
3. Yes.
4. Correct.

 

[santa]

Diy audio "baby huey el84"
This is possibly the best sounding amp i have built
I have built rh84, rh88, rh universal, kegger kt88 and was stunned at the sound quality of the baby huey

 

[Squidward]

Similarities:

• They are both low-parts-count Single-Ended EL84 amps.
• Both use Schade style feedback.

Differences:

• RH-84 is pentode mode only. You can use any 10W-5K OPT. Pentode mode can potentially be slightly more powerful than UL or Triode modes of operation.
• KG-84 is native UL mode. You must have a OPT with a UL tap.
• KG-84 is switchable from UL to Triode mode. Triode is less powerful than UL, and has different sonics.
• KG-84 has a higher B+. This means more power is possible. I would think that even tho RH-84 is pentode, the wattage will be similar because KG-84 has higher B+. it will be close in any case (4-5 WPC for either design).
• KG-84 has a wider choice of driver tube (6AQ8, 6DJ8, 6BK5, 6BQ7).

You could use the same power supply for either design, as long as it was capable of 330 VDC B+. You could always do different things to lower it from 330 to 300 if you wanted to try both designs.

I have built both from scratch. They're both good designs. If I had OPTs that did not have a UL tap, I would build the RH-84. If I had UL taps, I would build the KG-84. If I had to purchase OPTs new, I would purchase ones with UL screen taps for maximum flexibility.

 

[macaltec]

Thanks to all.

Squidward, very important info on the UL taps for the OPT.

1) I see the wattage and voltage is not specified on the KG-84 components, should I be brushing up on my math skills?
2) The RH84 does not specify wattage on some resistors, is there a minimum standard requirement here?
3) Just to be perfectly clear, for my own sanity, either design will accpet my 7189's without modification to the circuit?
4) What other driver tubes will the KG-84 accept? 12AU7? Mods needed to use the 12AU7?
5) Any good tutorials on using PSUD2?

 

[Squidward]

1. Here is a screenshot of my notes from when I built the KG-84. If resistor wattage isn't listed, it defaults to half a watt.
2. The two amps use the same wattage in the same positions.
3. Both circuits are for EL-84. 7189 is tougher than EL-84. 7189 will be fine in an EL-84 circuit, but not the other way 'round.
4. 6AQ8, 6DJ8, 6BK7, 6BQ7. Keg never used 12A*7.

 

[macaltec]

The Hammond UL tapped OPTs I found gave me sticker shock. I was trying to find one from Edcor but didnt see one anywhere. Does anyone know if Edcor will make one or have any other suggestions?

 

[opa1]

https://www.edcorusa.com/gxse10-5k

 

[macaltec]

Thanks. I have seen that and it is my choice if I build the RH84. What I dont see is an option to have it wound with a UL tap and possibly 4 and 8 ohm taps as well. Or am I looking at this wrong?

 

[Squidward]

The primary on the Edcore has a "Screen" tap, that is the UL tap.

 

[macaltec]

Excellent. Things are starting to become much more clear now.

I have fiddled around with PSUD2 a bit and see how to change components and values but am still unsure of what specific criteria I need to be looking at in order of importance. I assume getting the proper voltage would be first. Not 100% confident on which boxes to check to see that info. I do have an idea though. I will dive in this weekend and try to learn more.

 

[macaltec]

Leaning strongly to the KG-84. So now I am getting down to a few more details concerning the choices I make with caps and resistors. I am thinking I read recently to make sure coupling caps and feedback resistors be paid special attention. Please offer suggestions as to what I should be looking to use for these components, be specific. Any other details I need to address in terms of better quality parts?

 

[Squidward]

Use a carbon comp. resistor for the feedback. Use a 5W non-inductive wirewound for the power tube cathode. Carbon film everywhere else.

You can start with Orange Drops or russian coupling caps, roll some more exotic ones later if you feel like it. One nice thing about this amp topology and the single coupling capacitor is you can really hear parts changes if they make a difference.

Use a motor run or film cap for the first cap in the power supply, hopefully it can be 10uF or below. Use a nice electrolytic bypassed with a film for the second stage.

 

[primosounds]

Leaning strongly to the KG-84. So now I am getting down to a few more details concerning the choices I make with caps and resistors. I am thinking I read recently to make sure coupling caps and feedback resistors be paid special attention. Please offer suggestions as to what I should be looking to use for these components, be specific. Any other details I need to address in terms of better quality parts?

I have also built many RH type and a few of Keggar's creations, and the difference between the 2 types are small. I tend to prefer using the 12at7 since there are so many iterations of that tube. But, If you are looking to get the "most" out of your amp the Russian teflon caps are very good, but very big. So you need to allow for its size. It also takes several weeks to ship from Eastern Europe. I also wanted to comment that IME, the power supply being the heart of the amplifier, requires special attention. Since you will be using high efficiency speakers any PS noise can be intrusive. To that end, i prefer the RH ps with two inductors. I also prefer pentode mode with a tweaked G2 supply. As the extra watt or 2 can be more than 20% more power. This will allow better control of your speakers which should improve soundstage and dynamics as well as better bass.

 

[macaltec]

@primosounds, I knew the LCLC PS would come up. I initially wanted to use that design for the same reasons you stated. The additional cost threw me off though. I have many more decisions to make and much more research than I originally thought before I order any parts.

Again, many thanks for all the help.

 

[primosounds]

@primosounds, I knew the LCLC PS would come up. I initially wanted to use that design for the same reasons you stated. The additional cost threw me off though. I have many more decisions to make and much more research than I originally thought before I order any parts.

Again, many thanks for all the help.

No prob. If you have been reading up, you will have come across the fact that since SE requires a steady current demand, as the tubes are always "on". Not like PP, which has the ps working between the 2 halves of the split phase. So, a choke's job is to filter AC and supply extra current via its magnetic field. This allows one to use smaller capacitance and higher quality, film caps in the ps. To me this makes the ps much more responsive and dynamic, allowing more detail and better imaging. In other words the ps is in lock step with the music, not waiting for caps to charge up.

 

[macaltec]

Most of my understanding right now is getting my parts list and suppliers in order. I wont even pretend to understand how or why these circuits work yet. Although I understand PS circuits better than I do the audio circuits. I am learning as I go. I have built a tube preamp and recapped a couple power supplies. Mostly dabbled a bit over the years without diving in to far. Hopefully this experience will grow my knowledge and I can start to take on other challenges in building and design. I think the biggest concern I have right now is getting the PS design right and understanding how to make it work for whatever audio circuit I should desire to use.

 

[primosounds]

If you have not tried psud2 to help model your power supply then you should download the program.It is free and safe. Also reading up on the old tube audio books which always have a chapter devoted to PS design. A very basic book is the ARRL handbook.

 

[macaltec]

I have PSUD2 and have figured out how to add and change components. I'm not sure what or where to be looking for the info I need after that. I think I see where B+ is but thats about all I know so far. I have a few books around here on amp building and some tube characteristics manuals. Like I said, I have dabbled a bit in the past. I can only read so much before I need to get hands on. I think Im close.