The difference in LF performance between the 15W GXSE and the 25W CXSE is rather substantial, hence my recommendation to go bigger.
Ah. If was going to purpose this amp for midrange and up in a biamped system, the other OT would be ok right?
As was already indicated, no problems at the bottom end, given bass info. will be absent. However, if you want to try for full HF extension to 20 KHz., a GNFB loop will have to be added to the RH807 design. As LOTS of folks hearing doesn't go there, the issue may easily be academic.
I do have the tubes to do the Citation design. The extra wiring doesn't bother me, I would probably spin a PCB to avoid all the PP soldering.
Are you encouraging me towards the Citation knockoff? Would I stick with the 1625's? I don't think I have enough 6L6's in the stash.
Edit: I think I just will try the SE amp first. I already have a RAM RM9 as my main amp. Don't think I am compelled to build a new PP amp for now.
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I was showing cost/benefit, when I mentioned the Cit V.
As you are aiming at a multi-amped setup, continue on the SE path using GXSE O/P "iron". If top-end extension proves inadequate, we'll collectively tackle the issue of adding a GNFB loop.
As you are aiming at a multi-amped setup, continue on the SE path using GXSE O/P "iron". If top-end extension proves inadequate, we'll collectively tackle the issue of adding a GNFB loop.
I really appreciate the help and advice from you gentlemen.
I am leaning towards getting CXSE to avoid future regrets. Sometimes an extra $100 is not a bad price to pay for that. I've learned similar lessons in other projects I have undertaken.
I am leaning towards getting CXSE to avoid future regrets. Sometimes an extra $100 is not a bad price to pay for that. I've learned similar lessons in other projects I have undertaken.
The CXSE would give you "full" extension at both frequency extremes and allows you to try various things, including different speakers. 🙂 
As Keith Fenner says in the machine shop context, "Better to be looking at it than looking for it". Unused reserves of capability are not problematic, while lack of capability definitely is troublesome.
As Keith Fenner says in the machine shop context, "Better to be looking at it than looking for it". Unused reserves of capability are not problematic, while lack of capability definitely is troublesome.
Have followed the thread I think it is good that you choose to use CXSE I have used XSE for my EL84 but I lack some extension in both directions. Now one should not interpret this as if the smaller OPTs from Edcor are worse not at all they are very good for the money.
Good luck with your build!
Good luck with your build!
Resistors: On the SE807 design, I assume only the screen and 807 cathode resistor need to be power resistors? The rest metal film?
Capacitors: I assume the .22uf coupling capacitor should be a high quality (Auricap or similar) film. What about the bypass on the 807 cathode and the 33uf to ground on the plate supply to the ECC81?
Capacitors: I assume the .22uf coupling capacitor should be a high quality (Auricap or similar) film. What about the bypass on the 807 cathode and the 33uf to ground on the plate supply to the ECC81?
No need to spend a lot on a coupling capacitor. Either a 716P series "Orange Drop" or a Soviet surplus K40 paper in oil (PIO) will be fine.
This part is "perfect" for the O/P tube cathode bypass capacitor.
For PSU and decoupling duty, Nichicon or Panasonic 105o C. rated 'lytics get the nod.
1% metal film resistors in grid to ground and feedback positions. Carbon composition for the 200 Ω grid "stopper". Carbon film, whenever possible, everywhere else. No metal oxide parts in this build.
This part is "perfect" for the O/P tube cathode bypass capacitor.
For PSU and decoupling duty, Nichicon or Panasonic 105o C. rated 'lytics get the nod.
1% metal film resistors in grid to ground and feedback positions. Carbon composition for the 200 Ω grid "stopper". Carbon film, whenever possible, everywhere else. No metal oxide parts in this build.
I usually go through eBay... they are on Ali too...
I bought this listing: 50Pcs 0.01uf-0.47uf 10NF-470NF 275VAC 275V 10MM X2 Polypropylene Film Capacitor | eBay
I bought this listing: 50Pcs 0.01uf-0.47uf 10NF-470NF 275VAC 275V 10MM X2 Polypropylene Film Capacitor | eBay
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Eli, sorry to question you. Is there a reason for an 85°C rated part taking cathode bypass duty? I tend to use these guys:
https://www.mouser.co.uk/ProductDetail/KEMET/PEG124PD247VQL1?qs=DqLQsTv2bi6RuERTb5ii2w==
I know they are wayyy more pricy but TBH for longevity it's worth it.
Cheers
Matt
https://www.mouser.co.uk/ProductDetail/KEMET/PEG124PD247VQL1?qs=DqLQsTv2bi6RuERTb5ii2w==
I know they are wayyy more pricy but TBH for longevity it's worth it.
Cheers
Matt
I can't argue about the longevity factor, but ripple current (a cap. "killer") is not a factor here. Nichicon UKZ (Muse) series 'lytics have a solid reputation, when placed in the signal path. UKZ parts are specifically intended for audio service. Check the datasheet out.
FWIW, Jim McShane uses a UKZ in the bias supply of reworked H/K Cit 2. amps.
Thanks, I just wondered. Good choice as it's in the signal path. Space it away as best you can from the socket and cathode resistor without going crazy then🙂
Cheers
Matt
Cheers
Matt
Eli, just to clarify, wirewounds for the plate and cathode resistors for the ouput tube or no?
You can use Mills non-inductive (Aryton-Perry) MRA-12 parts for the O/P tube cathode resistors, but they are pricey. The exact value for Mills is 402 Ω and Michael Percy is a source.
I came up with this part in "ordinary", inductive, construction. A slight increase in the value of the bypass cap. is technically needed, but nothing additional might be just fine in the real world.
I came up with this part in "ordinary", inductive, construction. A slight increase in the value of the bypass cap. is technically needed, but nothing additional might be just fine in the real world.