Hey all,
I received a power transformer from Heyboer today. So this weekend I'm going to start an RH83 PPE SE amp. It should be good for about ten watts. Its a slight modification of Aleksandar's RH84 PPE amp.
Its a parallel SE design. I've made some slight modifications, Some at his suggestion. He built the original using 6AU6 and EL84. I will be using his circuit as designed for EF86. I recently received four 'Winged C' EF86 which I've tried in another amp to make sure they are not microphonic. Aleksandar suggested EF86 would be better than 6AU6. I'm using 6P15P/SV83 instead of EL84 hence RH83, (Because I have a bunch of them). He also suggested using LT1086 instead of 78L05 regulators for the cathodes of the outputs.
I've attached a picture of the chassis. To my knowledge this amp hasn't been built before so it should be interesting, at least for me!
I received a power transformer from Heyboer today. So this weekend I'm going to start an RH83 PPE SE amp. It should be good for about ten watts. Its a slight modification of Aleksandar's RH84 PPE amp.
Its a parallel SE design. I've made some slight modifications, Some at his suggestion. He built the original using 6AU6 and EL84. I will be using his circuit as designed for EF86. I recently received four 'Winged C' EF86 which I've tried in another amp to make sure they are not microphonic. Aleksandar suggested EF86 would be better than 6AU6. I'm using 6P15P/SV83 instead of EL84 hence RH83, (Because I have a bunch of them). He also suggested using LT1086 instead of 78L05 regulators for the cathodes of the outputs.
I've attached a picture of the chassis. To my knowledge this amp hasn't been built before so it should be interesting, at least for me!
Attachments
I am referring to this schematic: RH Amplifiers: RH84 PPE – "Parallel Pentode Edition"
Main flaw is the pentode connected single end output stage without sufficient NFB.
This sort of circuit has high output impedance and therefore the load impedance i.e. speaker, which is not a constant impedance, affects the frequency response and distortion. Also the damping of the speaker cone is low.
If pentode output stage is used for hifi amplifier it requires some amount of GNFB.
Main flaw is the pentode connected single end output stage without sufficient NFB.
This sort of circuit has high output impedance and therefore the load impedance i.e. speaker, which is not a constant impedance, affects the frequency response and distortion. Also the damping of the speaker cone is low.
If pentode output stage is used for hifi amplifier it requires some amount of GNFB.
NFB of some kind is needed with a pentode O/P stage, but it need not be global. Without a substantial amount of NFB, damping factor will be wretched. FWIW, I'd use both a short, inner, loop and an outer, global, loop.
BTW, the screen grid in the 6П15П (6p15p) is fragile. That fragility can be dealt with, along with improving open loop linearity, by regulating g2 B+ with a VR150/0D3.
Actually, the local shunt feedback lowers the output impedance of the output pentode(s) to equal or lower than triode strapping it.
If one has a speaker that likes a current amplifier, then the "wretched" damping factor becomes a very good thing.
dave
Actually if the drivers have right specs and bass load for that kind of amp it is probably the best way to run a fullrange because HF response is (in most cases) improved in comparison to constant power or constant voltage drive.
Ok guys,
My first intention with this amp was to build, as Eli calls it, a flea amp. But with around ten watts, say, a giant flea amp.
There are some things I like about this amplifier. That I have all the parts to build it. Also, I like the automatic bias system. And I prefer the use of zeners to limit screen voltage. I have some VR150's but the zeners seem much more simple. I have read that some do not like cathode regulation. And others that do not like the use of zeners.
I want to use SV83 instead of EL84. Because I have a bunch of them and I want to hear this tube in something. Is it possible to use this as an ultralinear configuration? And if so what would the proper tap percentage be? The figures I've seen most often are 20% or around 40%.
As for the feedback? From my limited experience feedback is in the final tuning. First you build the race engine. Then you put it on the dyno and tune the cam, ignition and fuel system parameters. It would be easy enough to add a GNFB feedback circuit once I have something to listen to.
I'll have to redraw the schematic and when I do I'll post it.
My first intention with this amp was to build, as Eli calls it, a flea amp. But with around ten watts, say, a giant flea amp.
There are some things I like about this amplifier. That I have all the parts to build it. Also, I like the automatic bias system. And I prefer the use of zeners to limit screen voltage. I have some VR150's but the zeners seem much more simple. I have read that some do not like cathode regulation. And others that do not like the use of zeners.
I want to use SV83 instead of EL84. Because I have a bunch of them and I want to hear this tube in something. Is it possible to use this as an ultralinear configuration? And if so what would the proper tap percentage be? The figures I've seen most often are 20% or around 40%.
As for the feedback? From my limited experience feedback is in the final tuning. First you build the race engine. Then you put it on the dyno and tune the cam, ignition and fuel system parameters. It would be easy enough to add a GNFB feedback circuit once I have something to listen to.
I'll have to redraw the schematic and when I do I'll post it.
Well, after the brain fart cleared I realized ultralinear with SV83 isn't a great idea. The differential between plate and G2 voltage makes it a non starter. Plus in pentode I'll have more gain to offset any additional feedback I might have to add.
So Eli's idea of using VR150 is a good one. From what I remember 18ma is right in the center of VR150's range. Eli, once upon a time I remember you mentioned a way to keep the VR from introducing any noise. Do you remember what that was?
So Eli's idea of using VR150 is a good one. From what I remember 18ma is right in the center of VR150's range. Eli, once upon a time I remember you mentioned a way to keep the VR from introducing any noise. Do you remember what that was?
Given that you are building an RH I'm not sure the ultra-linear buys you anything, and would probably reduce the effectiveness of the internal feedback due to the gain lost to the UL connection. It might be a wash linearity wise, but power output would be reduced due to the screen voltage rating. The point of the internal feedback path is to lower the plate resistance substantially and to improve the overall linearity of the amplifier.
The main issue is the very low voltage rating of the SV83 screens - in UL connection you would have to lower the B+ considerably, to no more than the screen rating of 200V, and power output would be greatly reduced as a result. I can't imagine that transformers with separate UL windings are in the budget.
The main issue is the very low voltage rating of the SV83 screens - in UL connection you would have to lower the B+ considerably, to no more than the screen rating of 200V, and power output would be greatly reduced as a result. I can't imagine that transformers with separate UL windings are in the budget.
Two in parallel ought to get fairly close if he runs close to the tube's limit. (I get ~5W out of a single 6V6 at 250V and 50mA combined screen and plate current, no red plating)
I would either build it as designed or not bother at all.
Funny enough, those that have I have contacted that stuck to the schematics and avoided "better" ideas seem to be very happy. Every amp that has been criticized seems to have NOT been an "original".
I love people who state facts with no reference to anything - especially experience with the item being criticized. I guess good distortion is like good cholesteral......
Funny enough, those that have I have contacted that stuck to the schematics and avoided "better" ideas seem to be very happy. Every amp that has been criticized seems to have NOT been an "original".
I love people who state facts with no reference to anything - especially experience with the item being criticized. I guess good distortion is like good cholesteral......
rowuk,
I had this same... discussion with Aleksandar. He's not speaking to me anymore. I'm in this to learn and have fun. I've built two RH84's per the schematic and they were nice amps. But its more fun for ME to modify existing designs. First, because its more interesting than mere production. And second, I learn more that way.
Amateur math here, (read guess) two EL84 dissipate 28 watts. Two SV83 dissipate 27. Less than a four percent difference. I know that dissipation is related to power output. And in the original SPICE model 11.06 watts is predicted. 94% of 11.06 is 10.4. So 10.4, 10, 9.7 not a lot of difference there. But my RH84's were good for about 4 watts. So I expect a 3db gain and that should be worth it. The quest is the thing.
I had this same... discussion with Aleksandar. He's not speaking to me anymore. I'm in this to learn and have fun. I've built two RH84's per the schematic and they were nice amps. But its more fun for ME to modify existing designs. First, because its more interesting than mere production. And second, I learn more that way.
Amateur math here, (read guess) two EL84 dissipate 28 watts. Two SV83 dissipate 27. Less than a four percent difference. I know that dissipation is related to power output. And in the original SPICE model 11.06 watts is predicted. 94% of 11.06 is 10.4. So 10.4, 10, 9.7 not a lot of difference there. But my RH84's were good for about 4 watts. So I expect a 3db gain and that should be worth it. The quest is the thing.
Built an EF86/EL84 RH.
Ohhh whats the distortion level..
don't care.
Whats it sound like...I like it, great fun to build.
Changed the bypass cap on the OP tube made quite a difference.
How often do I use it...most days.
Do I have better amps...yes..why do you use the RH...there is something about it I like.
Does the RH deserve the bashing it gets<<no..it might fill a gap that some people want.
That amp sounded quite bright at first then settled down after a couple of months. Might be the old Ef86's.
Component choice (I think) is important.
I would build the universal RH...time is a factor at the moment!
Regards
M. Gregg
Ohhh whats the distortion level..
don't care.Whats it sound like...I like it, great fun to build.
Changed the bypass cap on the OP tube made quite a difference.
How often do I use it...most days.
Do I have better amps...yes..why do you use the RH...there is something about it I like.
Does the RH deserve the bashing it gets<<no..it might fill a gap that some people want.
That amp sounded quite bright at first then settled down after a couple of months. Might be the old Ef86's.
Component choice (I think) is important.
I would build the universal RH...time is a factor at the moment!
Regards
M. Gregg
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