rh84 build/design questions

[jollyrogr]

So as I await my edcor transformers to finish my budgie SE, I've been reading about the RH84 and how much people love it. I think this will have to be my next project. Some questions I have about it though...

1. Can you add a volume pot? Whats the recommended way of doing that?

2. I've seen some discussion about different power supply configurations, what's the way to go?
2b. Are there certain caps that work better than others? Solen?

3. Worth it to rectify the heaters to minimize hum?

Thanks guys

I spose I should put in another order to Edcor right away

[kheper]

So as I await my edcor transformers to finish my budgie SE, I've been reading about the RH84 and how much people love it. I think this will have to be my next project. Some questions I have about it though...

1. Can you add a volume pot? Whats the recommended way of doing that?

Yes. Attach it right after the input jacks.

2. I've seen some discussion about different power supply configurations, what's the way to go?

It's impossible to say since you did not post links to different schematics. In general, I'd go with a solid state, Full Wave Bridge cap input design. Do not skimp by omitting the choke.

http://tubes.nekhbet.com/#fulb

2b. Are there certain caps that work better than others? Solen?

Caps are subjective. I've heard Solon "Fast" caps praised and damned. Orange drops should be fine.

3. Worth it to rectify the heaters to minimize hum?

Sounds like overkill for an EL84 amp.

Thanks guys

I spose I should put in another order to Edcor right away

[Alex Kitic]

So as I await my edcor transformers to finish my budgie SE, I've been reading about the RH84 and how much people love it. I think this will have to be my next project. Some questions I have about it though...

1. Can you add a volume pot? Whats the recommended way of doing that?

Yes. Attach it right after the input jacks.

But not instead of the bleeding resistor on the input tube!

Since the input sensitivity of the RH84 is quite high (i.e. in the 775mV class) you can add input cinches, a selector, and a pot - transforming it into an integrated amp.

2. I've seen some discussion about different power supply configurations, what's the way to go?

It's impossible to say since you did not post links to different schematics. In general, I'd go with a solid state, Full Wave Bridge cap input design. Do not skimp by omitting the choke.

http://tubes.nekhbet.com/#fulb

While you cannot go wrong with the suggested power supply (the choke should be 100mA since it is shared by both channels), LCLC sounds better, but adds to the cost by introducing an additional choke, possibly higher quality than the standard choke to be used between the caps. Of course, the HT secondary needs to have higher AC voltage, although AC current can be 30% less with choke input, i.e. 100mA rated HT secondary would suffice for a choke input.

The rectifier choice is yours to make, but tube rectifiers sound WAY BETTER than solid state diodes. SS diodes ONLY if you cannot afford the additional cost of a rectifier and its heater secondary...

In my view and experience it is better to save on electrolytic caps (buy normal current production small in size large in capacity) than to save on the rectifier tube.

While the design gives you some shortcuts towards good sound, there are elements that influence the final result which cannot be quantified as schematic plots (but the significance of which can be scientifically proven through analysis).

2b. Are there certain caps that work better than others? Solen?

Caps are subjective. I've heard Solon "Fast" caps praised and damned. Orange drops should be fine.

If we are talking about coupling caps, you can consider WIMA MKS and MKP as standard items for an RH84 (if it was a kit, those would be the caps).

My "better choice" would be styro caps, or Siemens poly in oil caps. It's obvious I crave for good bass :D

Regarding power supply caps, please read above.

3. Worth it to rectify the heaters to minimize hum?

Sounds like overkill for an EL84 amp.

There is absolutely no need to apply DC to heaters of indirectly heated tubes, unless it's a phono preamp. For line preamps and power amps, DC is an unnecessary complication with added parts and heat...

Therefore, not an overkill, but an unnecessary complication.

[kheper]

So as I await my edcor transformers to finish my budgie SE, I've been reading about the RH84 and how much people love it. I think this will have to be my next project. Some questions I have about it though...

1. Can you add a volume pot? Whats the recommended way of doing that?

Yes. Attach it right after the input jacks.

But not instead of the bleeding resistor on the input tube!

I was going to suggest a value, a brand and tell him how to hook it up in my follow up response. By scrawling too many paragraphs in one post, people just ignore them.

2. I've seen some discussion about different power supply configurations, what's the way to go?

It's impossible to say since you did not post links to different schematics. In general, I'd go with a solid state, Full Wave Bridge cap input design. Do not skimp by omitting the choke.

http://tubes.nekhbet.com/#fulb

While you cannot go wrong with the suggested power supply (the choke should be 100mA since it is shared by both channels), LCLC sounds better, but adds to the cost by introducing an additional choke, possibly higher quality than the standard choke to be used between the caps. Of course, the HT secondary needs to have higher AC voltage, although AC current can be 30% less with choke input, i.e. 100mA rated HT secondary would suffice for a choke input.

I think 100ma is a bit current shy for a stereo EL84 amp.

http://tubes.nekhbet.com/#fulbc

A Full Wave Bridge choke input design with a 350Vac @ 140ma transformer will suffice to produce 315Vdc @(better than)200ma. Very good regulation at a reasonable cost. Antek has such a transformer.

http://www.antekinc.com/details.php?p=1111

[Alex Kitic]

I think 100ma is a bit current shy for a stereo EL84 amp.

Well, I designed this one (RH84) so I should know whether it is enough, or not, shouldn't I?

Anode dissipation of the EL84 is 12W, at 300V across the tube thus leaves us with 40mA... the driver draws approximately 3mA, that's some 45(ish) mA per channel, if you count in the current drawn by g2. Stereo=2 channels, i.e. RH84 current draw approx. 90mA.

Therefore, a 100mA choke is just fine.

Not to mention the fact that at 100mA one can use a 5Y3 or 80 as rectifier, which should lead to great listening happyness :D

A Full Wave Bridge choke input design with a 350Vac @ 240ma transformer will suffice to produce 315Vdc @(better than)220ma. Very good regulation at a reasonable cost. Antek has such a transformer.

http://www.antekinc.com/details.php?p=0

Your suggestion might work fine with the RH Universal if one would not want to stick to the schematics, or would deliberately want to loose the "universality" given by the combination of constant current draw and variable B+ dependent on the type of tube rectifier used...

But this thread is about the RH84, not the RH Universal...

[kheper]

I think 100ma is a bit current shy for a stereo EL84 amp.

Well, I designed this one (RH84) so I should know whether it is enough, or not, shouldn't I?

Anode dissipation of the EL84 is 12W, at 300V across the tube thus leaves us with 40mA... the driver draws approximately 3mA, that's some 45(ish) mA per channel, if you count in the current drawn by g2. Stereo=2 channels, i.e. RH84 current draw approx. 90mA.

Therefore, a 100mA choke is just fine.

I take your word for it, but most of the datasheets show ~50ma current draw per EL84. Plus, a cushion of current capacity is desirable, though more expensive.

A Full Wave Bridge choke input design with a 350Vac @ 240ma transformer will suffice to produce 315Vdc @(better than)220ma. Very good regulation at a reasonable cost. Antek has such a transformer.

http://www.antekinc.com/details.php?p=0

Your suggestion might work fine with the RH Universal if one would not want to stick to the schematics

That was my initial point. What schematic does he intend on using? Is the following the original? FW cap input at ~300Vdc.

http://www.tubeaudio.8m.com/RH84/rh84.html

[jollyrogr]

That was my initial point. What schematic does he intend on using? Is the following the original? FW cap input at ~300Vdc.

I was going to use this one

I was going to suggest a value, a brand and tell him how to hook it up in my follow up response. By scrawling too many paragraphs in one post, people just ignore them.

I was thinking ALPS 100k log taper?

Not to mention the fact that at 100mA one can use a 5Y3 or 80 as rectifier, which should lead to great listening happyness :D

so is the 5Y3 rectifier tube better than the 5U4 shown in the schematic?

I do plan to stick with valve rectification rather than SS.

While you cannot go wrong with the suggested power supply (the choke should be 100mA since it is shared by both channels), LCLC sounds better, but adds to the cost by introducing an additional choke, possibly higher quality than the standard choke to be used between the caps. Of course, the HT secondary needs to have higher AC voltage, although AC current can be 30% less with choke input, i.e. 100mA rated HT secondary would suffice for a choke input.

Whats that look like in a schematic?

Thanks for all your help so far!

[kheper]

I do plan to stick with valve rectification rather than SS.

While you cannot go wrong with the suggested power supply (the choke should be 100mA since it is shared by both channels), LCLC sounds better, but adds to the cost by introducing an additional choke, possibly higher quality than the standard choke to be used between the caps. Of course, the HT secondary needs to have higher AC voltage, although AC current can be 30% less with choke input, i.e. 100mA rated HT secondary would suffice for a choke input.

Whats that look like in a schematic?

In the schematic, the power supply is a tube, Full Wave capacitor input CLCC design. There is no current rating given for the transformer. With a Full Wave cap input, the Iac=Idc. Do NOT go with a transformer rated at less than 100ma. (I would try to find a 150ma or better.)

[kheper]

While you cannot go wrong with the suggested power supply (the choke should be 100mA since it is shared by both channels), LCLC sounds better, but adds to the cost by introducing an additional choke, possibly higher quality than the standard choke to be used between the caps. Of course, the HT secondary needs to have higher AC voltage, although AC current can be 30% less with choke input, i.e. 100mA rated HT secondary would suffice for a choke input.

I think 100ma is a bit current shy for a stereo EL84 amp.

I think 100ma is a bit current shy for a stereo EL84 amp.

Well, I designed this one (RH84) so I should know whether it is enough, or not, shouldn't I?

Anode dissipation of the EL84 is 12W, at 300V across the tube thus leaves us with 40mA... the driver draws approximately 3mA, that's some 45(ish) mA per channel, if you count in the current drawn by g2. Stereo=2 channels, i.e. RH84 current draw approx. 90mA.

Therefore, a 100mA choke is just fine.

Hold on. I was referring to the max current rating of the B+ supply, not the choke. An amp with 90ma as the very lowest current draw needs a supply that can shell out more current than 100ma.

[Alex Kitic]

OK, kheper... I think it's time to end this argument. Your comments are not clear enough nor directly related to the subject, i.e. an advice request by a diyer who would like to build an amp (happens to be the RH84).

1) I really do not know how knowledgeable you are about electronics and stuff, but I am under the impression that for you this is just a hobby. There is nothing wrong with that, but you should try not to mislead other people with your own beliefs which may or may not be correct.

2) This is evident in the story about power supply requirements (B+ current) of amplifiers. You seem to mix class A and class AB, SE and PP operation... a class A SE amp will tend to draw a given current regardless of the state of operation, i.e. excited by signal or just sitting down powered. Therefore, a SE amp which by definition can operate only in class A since there is only one active device amplifying the signal, will draw approximately the same current all the time. If this current is 90mA, it is safe to assume that there is no reason why this amp should require a current reserve of some particular magnitude. Furthermore, the supply caps capacity can be determined quite easily, since the amplifer needs a given amount of J (Joule) to operate... etc. Most power supplies, like the one originally incluede with the RH84 schematics, are quite up to the job they are required to do. Lowering the power supply impedance will yield improved results, but those are issues of finesse, not operation.

BTW, I have noticed in another thread that you have not immediately recognized that it was about an SE amp - you tought it was a PP amp... you seem to favour them, at least as a way of tought.

3) Recommendations given in datasheets are what the word says - recommendations. Must be taken into consideration carefully. If 50mA current draw is mentioned, it is obvious that Ua will not be 300V as that would mean 15W, too much for a 12W anode dissipation tube (Pa).

Design choices, on the other hand, are not recommendations. They are consciously made by people who design (amplifiers, in this case). I chose higher voltage, higher primary anode load, lower current - just like in RH Universal I chose lower voltage, lower anode load, higher current operation.

4) I can't escape the impression that you have not built any RH amp, and particularly not the RH84. Many diyers have built it without making too much fuss about it, often with scrap box parts, or recycling other amps and consoles... and I have yet to read that someone was not satisfied with the results. Those who invested more in parts, tube, and general craftsmanship quality were rewarded beyond their expectations.

Therefore, please let us stop this unnecessary argument and stop cluttering this thread with our discourse. Jollyrogr started this thread to get some advice, presumably from people who built it and can give such advice. Let him get some GOOD advise.

[jollyrogr]

So this should be a good fit for a PT right? http://www.edcorusa.com/p/597/xpwr008_120

For the LCLC, what values for the chokes and caps?

[jollyrogr]

Thanks Alex, why chose a 5Y3 over 5U4? Still learning about the myriad of tubes available.

[Alex Kitic]

I was going to use this one...

Yes, good choice :) with corrected current value for the choke.

I was thinking ALPS 100k log taper?

Blue velvet would be just fine, 100k is a good value - as I said previously, add a selector and several pairs of cinch connectors and you got yourself a valid integrated amp.

so is the 5Y3 rectifier tube better than the 5U4 shown in the schematic?

I do plan to stick with valve rectification rather than SS.

Whats that look like in a schematic?

For the CLCL just take another 100mA choke (BTW, no need for 20H, 5-10H is actually more than enough per choke) and place it between the first cap and the rectifier output.

This will require an increase in HT secondary voltage, but allow a decrease of HT secondary current, as already mentioned in the thread. With choke input, the HT secondary needs to be no more than 100mA AC, while for cap input the HT secondary needs to be about 140mA. More is OK in either case, but there is no need for overkill.

Last but not least, the recommended 5Y3 has a higher voltage drop compared to 5R4 or 5U4, therefore you will need a higher HT secondary for 5Y3 (or 80) operation.

I suggest you do some simulations with PSUD to determine the HT secondary voltage value. You need to have a B+ of 310-330V at the connection to the OPT primary. You can use a "constant current" load of 90mA to define the values more easily.

Good luck, and feel free to ask for advise!

[Alex Kitic]

Thanks Alex, why chose a 5Y3 over 5U4? Still learning about the myriad of tubes available.

Based on experience... I particularly like "tube rolling" rectifiers.

Black anode rectifiers give a more precise sound.
5R4 tends to be more precise and defined than 5U4.
5U4 gives the best overall sound, with black anodes it's precise enough yet tubey and tending towards warm.
5AR4 is generally dull and uninteresting, still beating solid state diodes by miles. Still, Philips and Mullard can be very interesting (but not worth the exorbitant price tag).
5Y3GT and 80 black anodes versions are among the very best preamp rectifiers around, and give particular finesse to lower powered amps that can use these tubes, like 2A3 in higher voltage lower current versions (300V50mA) and of course the RH84 :D
A personal favourite for preamps: 5W4.

I dislike: EZ80 and particularly EZ81 (that is why they were never mentioned as alternatives for RH84, although the EZ81 fits the bill perfectly in theory - noval socket, indirect heating (you could heat it from the same source as the other tubes at 6.3V), size... etc.

The above listing is meant to help and shows my preferences. While most will agree, some might have different impressions, dictated by the myriad of alternatives available...

[jollyrogr]

Ok, I installed PSUD but I'm not sure what I'm doing yet. I'll play around with it some more. What's the best way to draw up a new schematic? Any good free programs out there for that? I'd like to draw up a new one with my changes before I start building