Looking at the blurred Akai M5 schematic that I googled makes me think that a smaller reservoir cap ( 22uF ) should be used instead of the 47uF that is in the RH84 schematic.
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If my Duncan psu sim is correct the 22uF cap still gets you close to the 300Vdc B+
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Here is a better one.
Note that both channels are not the same.
The 1st cap shouldn't be so large as to exceed the rectifiers current rating.
dave
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I think I have that figured out. The 6x4 is rated to 40uF so I went with a 30uF filter cap. I originally decided to stay with the 6x4 because the Akai transformer's heater secondaries were the right value for it. Is there anything else I should be concerned about? Earlier in this thread someone said that the bias should be alright as is.
Hi Planet 10, That's much clearer, clear enough to notice it's a different schematic to the one I found. 😉
I presume that the audio output transformers are identical and suitable for service in the RH84. Nearly made that mistake with a Telefunkin console, one channel was normal the other was for a bass woofer!
Hi Harmolodics, If your B+ is around 300Vdc then I would stick with the 270 Ohm cathode resistor. Tweeking can come later 🙂
I'm guessing that the extra bits in the top channel are to drive one or more of the tape-heads -- it is a power pentode sometimes seen in SE output stages.
I have 6 channels of these, for at least the 1st pair i'll do an RH84 varient.
dave
Finished Mono RH84s
Took a lot longer than I thought, but I'm happy with the result. Haven't gotten to hear them much because my speakers aren't done yet. But they worked when I tested them. They both buzz when the input is disconnected, but are otherwise quiet. Is that common? I haven't found to much information on troubleshooting this issue.
Took a lot longer than I thought, but I'm happy with the result. Haven't gotten to hear them much because my speakers aren't done yet. But they worked when I tested them. They both buzz when the input is disconnected, but are otherwise quiet. Is that common? I haven't found to much information on troubleshooting this issue.
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Hey RH guys,
I bought a Zenith 5L29 console amp. Everyone on another thread said to RH it. This is a budget project for a friend so new transformers are out. Problem is the power transformer delivers more like 370 volts unloaded. The 5L29 runs 350 B+ and 310 on the screens. I know modern EL84's won't take that kind of voltage. I have a pair of vintage 6BQ5/EL84's that came with a Sansui integrated. I haven't tested them yet but was hoping to use those. They are branded RTN? If they aren't any good how about 6P14P? 7189A? And if I ran that kind of B+ would the circuit have to be modified? Especially cathode resistor?
Kevin
I bought a Zenith 5L29 console amp. Everyone on another thread said to RH it. This is a budget project for a friend so new transformers are out. Problem is the power transformer delivers more like 370 volts unloaded. The 5L29 runs 350 B+ and 310 on the screens. I know modern EL84's won't take that kind of voltage. I have a pair of vintage 6BQ5/EL84's that came with a Sansui integrated. I haven't tested them yet but was hoping to use those. They are branded RTN? If they aren't any good how about 6P14P? 7189A? And if I ran that kind of B+ would the circuit have to be modified? Especially cathode resistor?
Kevin
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RH84 v.2
Hello!
I'm interested in the application using 6AU6 as driver...knowing it couldn't be the best solution, still I have a few 6AU6's (and 12AU6's also) and I want to get them to work...can I get the schematic practically used?
I saw somebody saying about use of EC92, yes, it's fully equivalent to half of 12AT7/ECC81, usually I replaced the rare EC92 with half of ECC81 and worked the same in old radios...
The original version, using two trides in the same bulb is easier to build, for those who intend to build separate monoblocks or amplified speakers, the EC92 is the perfect replacement...also the 12AT7 with paralleled triodes would be an interesting solution...I also tried the ECC88 paralleled and the sound is very good, even with the cheap Edcor transformers.
Now I intend to build the second version of RH84, using zenner diode for G2 and LM317 as current sink for EL84. The output transformers will be some salvaged parts from an old german radio...also the power transformer will be from that radio (Capri Grossuper, DDR made). The original voltage was around 280V, but using old selenium rectifier, I expect close to 300V B+ using modern diodes...
The "Capri" transformers are designed for the original 6 ohms output, with four interleaved windings, 2X1450 turns for primary, serries coupled, and two 103 turns for the secondary, paralelled. The secondary windings are accessible, with four wires separately, but the primary windings are internally coupled...with no easy exterior acces - only one isolated strap.
Any suggestions?
Hello!
I'm interested in the application using 6AU6 as driver...knowing it couldn't be the best solution, still I have a few 6AU6's (and 12AU6's also) and I want to get them to work...can I get the schematic practically used?
I saw somebody saying about use of EC92, yes, it's fully equivalent to half of 12AT7/ECC81, usually I replaced the rare EC92 with half of ECC81 and worked the same in old radios...
The original version, using two trides in the same bulb is easier to build, for those who intend to build separate monoblocks or amplified speakers, the EC92 is the perfect replacement...also the 12AT7 with paralleled triodes would be an interesting solution...I also tried the ECC88 paralleled and the sound is very good, even with the cheap Edcor transformers.
Now I intend to build the second version of RH84, using zenner diode for G2 and LM317 as current sink for EL84. The output transformers will be some salvaged parts from an old german radio...also the power transformer will be from that radio (Capri Grossuper, DDR made). The original voltage was around 280V, but using old selenium rectifier, I expect close to 300V B+ using modern diodes...
The "Capri" transformers are designed for the original 6 ohms output, with four interleaved windings, 2X1450 turns for primary, serries coupled, and two 103 turns for the secondary, paralelled. The secondary windings are accessible, with four wires separately, but the primary windings are internally coupled...with no easy exterior acces - only one isolated strap.
Any suggestions?
Hi Carageae,
Aleksandar designed this amp. It uses the 6AU6 as a driver with two EL84 in parallel. I've built two of Aleksandar's amps and can attest that they sound great. The two EL84's would also give you a little more power. You will find the schematic on Aleksandar's blog:
RH Amplifiers: August 2013
Kevin
Aleksandar designed this amp. It uses the 6AU6 as a driver with two EL84 in parallel. I've built two of Aleksandar's amps and can attest that they sound great. The two EL84's would also give you a little more power. You will find the schematic on Aleksandar's blog:
RH Amplifiers: August 2013
Kevin
Thank you! I was on that blog, but I skipped this version, maybe because of paralleling...EL84 is interesting as is, if I want more power I use EL34. Maybe EL34 paralleled could be interesting 😀
Well, the driver section could be used intact to drive a single EL84. Just remove the second output section and use a 5k output transformer.
Yes, I know...that's I intend to do. But first, I think I will make a test module with both drivers - ECC81 and 6AU6 to compare sound levels and quality. Or, at least, I will ask a friend to make a simulation of the two situations. If there is no important disadvantage in sound, I will use the pentodes...I have a few tubes almost new, even they were in some old equipment, but just ocasionally used.
For RH84 with Pentode driver, see also our earlier thread from 2011:
http://www.diyaudio.com/forums/tubes-valves/187441-rh84-se-pentode-driver-advice-please.html
http://www.diyaudio.com/forums/tubes-valves/187441-rh84-se-pentode-driver-advice-please.html
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