Hello DIY Peeps,
I am excited to share my first amp build in over 10 years.
It is the standard / original RH84 circuit.
I made the box from salvaged Urban Lumber (city tree that would have ended up in the landfill) and it is European Walnut.
The Aluminum Plates are 4mm thick and were made by Proto Panel. I was happy with PP's pricing and fast service. 1/2 the price of their competitor.
Playing around with aesthetics, I decided to hang the iron under the top plate, and hide all components except the tubes.
Room inside filled up much quicker than I expected.
I ended up having to mount a tag board directly over the heater wires, which I was worried about, but fortunately the amp is dead quiet.
This is my amp at work and replaces a mini watt EL84, which ironically got me interested in building again. Amazing little amp for $200.
The dynamics and extended frequency response (low and high) are greatly improved however I perceive a strange phase character in the sound. Literally like the speakers are connected out of phase, however they are connected in phase and the imaging is still quite good. Not really 3D like a DHT amp but still good. It is subtle but still quite apparent and a BIG distraction and very annoying! I guess you could also describe it like a reverb or delay effect pedal for a guitar.
Is this a function of the feedback in the circuit? Could it be a bad tube? I have swapped the 6bq5's without change in sound but only have one new production ecc81 at the moment.
Not sure if I am hearing the character of the amp that I don't like, or if it could be a build or component problem?
B+ is a little high at 324V with the specified 5U4 and 318V with the tube store 274b replacement (which sounds better).
I am assuming it's ok to run the EL84's a little hot? Or is a pair of 7189's worth the $?
I don't want to waste any more time or money on this amp if it is a characteristic of the feedback in the circuit that I don't care for. But I really have no idea...
I am surprised that so much of the mini watt magic has disappeared in exchange for better frequency response and dynamics.
Also, This amp is a warm up for some future builds so would appreciate any comments, suggestions on rookie mistakes or areas for improvement on basic layout or any other glaring build mistakes.
Next two amp builds will be a 45 and 6CB5A, both IT coupled Thomas Mayer designs.
Thank You for taking the time to read and for your comments!!!
I am excited to share my first amp build in over 10 years.
It is the standard / original RH84 circuit.
I made the box from salvaged Urban Lumber (city tree that would have ended up in the landfill) and it is European Walnut.
The Aluminum Plates are 4mm thick and were made by Proto Panel. I was happy with PP's pricing and fast service. 1/2 the price of their competitor.
Playing around with aesthetics, I decided to hang the iron under the top plate, and hide all components except the tubes.
Room inside filled up much quicker than I expected.
I ended up having to mount a tag board directly over the heater wires, which I was worried about, but fortunately the amp is dead quiet.
This is my amp at work and replaces a mini watt EL84, which ironically got me interested in building again. Amazing little amp for $200.
The dynamics and extended frequency response (low and high) are greatly improved however I perceive a strange phase character in the sound. Literally like the speakers are connected out of phase, however they are connected in phase and the imaging is still quite good. Not really 3D like a DHT amp but still good. It is subtle but still quite apparent and a BIG distraction and very annoying! I guess you could also describe it like a reverb or delay effect pedal for a guitar.
Is this a function of the feedback in the circuit? Could it be a bad tube? I have swapped the 6bq5's without change in sound but only have one new production ecc81 at the moment.
Not sure if I am hearing the character of the amp that I don't like, or if it could be a build or component problem?
B+ is a little high at 324V with the specified 5U4 and 318V with the tube store 274b replacement (which sounds better).
I am assuming it's ok to run the EL84's a little hot? Or is a pair of 7189's worth the $?
I don't want to waste any more time or money on this amp if it is a characteristic of the feedback in the circuit that I don't care for. But I really have no idea...
I am surprised that so much of the mini watt magic has disappeared in exchange for better frequency response and dynamics.
Also, This amp is a warm up for some future builds so would appreciate any comments, suggestions on rookie mistakes or areas for improvement on basic layout or any other glaring build mistakes.
Next two amp builds will be a 45 and 6CB5A, both IT coupled Thomas Mayer designs.
Thank You for taking the time to read and for your comments!!!
Really lovely wood. That's a pretty impressive looking "first time" build. Can't quite make out the name on those big blue caps?
Almost sounds like "one" speaker is out of phase.
jeff
The bass will sound much tighter than most other SE amps which could account for your perceived phase issue. In my Schade feedback amps the bass approaches that of a typical SS amp and is quite different to the underdamped sound of most tube amps. This will be heard as a loss of bass and a thinning out of the overall sound.
Nice build.
Shoog
Nice build.
Shoog
I agree with Shoog. I think the typical tube amp gives that underdamped bass response that we often perceive as bass which in reality is a speaker that is not well controlled in the lower frequencies and gets "boomy".
I have built a few RH amps and have not experienced what you are describing.
The B+ of 324Vdc does not mean much on its own. You need to measure the cathode voltage and and calculate the EL84 dissipation.
I would hazard a guess you are at about 11 - 12 volts at the cathode and I think its a 270R cathode resistor. Current is probably 40mA - 45mA, maybe more. You are probably over the EL84 dissipation. Measure it and make sure. If you are, drop your B+ or easier put in a slightly higher cathode resistor, try 300R
Depending on what you used for opt's, EL84 current draw and how loudly you play music maybe you are saturating the opt's and that is causing the bass issue?
Great looking amp!
I have built a few RH amps and have not experienced what you are describing.
The B+ of 324Vdc does not mean much on its own. You need to measure the cathode voltage and and calculate the EL84 dissipation.
I would hazard a guess you are at about 11 - 12 volts at the cathode and I think its a 270R cathode resistor. Current is probably 40mA - 45mA, maybe more. You are probably over the EL84 dissipation. Measure it and make sure. If you are, drop your B+ or easier put in a slightly higher cathode resistor, try 300R
Depending on what you used for opt's, EL84 current draw and how loudly you play music maybe you are saturating the opt's and that is causing the bass issue?
Great looking amp!
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I think that it was George at tubelab who had mentioned that he had put through a larger than usual amount of voltage (well, come to think of it, since when has it not been the case when George at tubelab has put more voltage through a tube???) through an EL84 tube without too much consequence.
However, I believe George at tubelab noted that when it came to the JJ EL84 tubes, the rugged/taller/thicker/wider plated EL84 could handle much more than he expected. The other smaller plated JJ EL84 couldn't do the same.
Nice looking amp by the way.
However, I believe George at tubelab noted that when it came to the JJ EL84 tubes, the rugged/taller/thicker/wider plated EL84 could handle much more than he expected. The other smaller plated JJ EL84 couldn't do the same.
Nice looking amp by the way.
Thanks for the kind words and replies!
I built the original RH version, without sand.
I have traced the circuit several times and everything appears to be correct. Also I made sure I didn't mix up Left and Right channel connections.
I've tried every speaker connection possible and I am definately connected "in Phase".
Shoog, Andrew, thanks for your input.
I think you are correct and I may just not be use to the sound. I mean the amp sounds amazing, there is just a subtle characteristic that sounds odd to me.
I did dig up a NOS 12AT7 and also found a 6201 this morning, to replace the JJ tube. This seams to make some difference, although I still hear a bit of "thiness" in the vocal region.
I'll take some more measurements when I have a chance, to make sure I am not over the EL84 dissipation. It could certainly be this too.
OPT's are 10W transcendars.
I am not listening too loud however the amp is running at 1/2 to 3/4 full throttle. Speakers are alpair 6P which are 4ohms and not the most efficient of Mark's offerings.
I also added a volume pot. I replaced the 1M resistor at input with a 100K Pot. Is this the correct way to wire this into the circuit, and proper impedance for a 2V source?
Thanks Again!
I built the original RH version, without sand.
I have traced the circuit several times and everything appears to be correct. Also I made sure I didn't mix up Left and Right channel connections.
I've tried every speaker connection possible and I am definately connected "in Phase".
Shoog, Andrew, thanks for your input.
I think you are correct and I may just not be use to the sound. I mean the amp sounds amazing, there is just a subtle characteristic that sounds odd to me.
I did dig up a NOS 12AT7 and also found a 6201 this morning, to replace the JJ tube. This seams to make some difference, although I still hear a bit of "thiness" in the vocal region.
I'll take some more measurements when I have a chance, to make sure I am not over the EL84 dissipation. It could certainly be this too.
OPT's are 10W transcendars.
I am not listening too loud however the amp is running at 1/2 to 3/4 full throttle. Speakers are alpair 6P which are 4ohms and not the most efficient of Mark's offerings.
I also added a volume pot. I replaced the 1M resistor at input with a 100K Pot. Is this the correct way to wire this into the circuit, and proper impedance for a 2V source?
Thanks Again!
I kept the 1M in mine after the pot. It will provide a ground reference for the grid in case the pot's wiper loses contact (what with oxidation and such).
Thanks KEVIN !
Skimming through the thread using my iPhone during smoke break. Sorry!
I've built several rh84 using the exact transcendar OPTX, I like what I've heard but with efficience speakers, i never had it playing with anything below 96db speakers. So I would say to try it out on some thing more efficience after you have the voltage dial in.
Skimming through the thread using my iPhone during smoke break. Sorry!
I've built several rh84 using the exact transcendar OPTX, I like what I've heard but with efficience speakers, i never had it playing with anything below 96db speakers. So I would say to try it out on some thing more efficience after you have the voltage dial in.
Hello,
Dont want to start new thread so please bear with me. I already have 12AT7 and EL84 tubes, Can anyone answer few questions (Newbie here).
1) I have an old transformer used in valve amps. The secondary leads is showing 360 V. The RH84 amplifier suggests B+ 315V. Will it be ok to use 360v ? Heater supply is OK (6.3v). Any clever way to drop the voltage OR use some of that voltage somewhere usefull to drop it ? Dont want to put heating resistor.
2) We already have 230V Mains power line is there any other option (Like solid state circuit etc. ) to get around 315 directly from mains line. So I can avoid using old transformer ?
3) I also have two tiny chokes with 4A written on it. Size is approximately 2 inches width x 1 inch height) I doubt the marking '4A' are amperes. Probably they are salvaged from old radio. Can I use them in power supply as filters ? Dont have inductance meter.
4) I have read about the RH84 amp and I know original designer Alex Kitic strongly recommends rectifying valve But valve sellers here are demanding Big money for untested old valves. So can I replace it with SS rectifier.
5) A SS powersupply schematic will be great. That way I can avoid transformer, rectifier issues. Probably chokes too ?
6) Also have some (have 3 leads) pushpull output transformer. Can they be used just to get the 'sound taste' of valve sound ? 5K-8K is written on it.
Please give me suggestions, hints, guidelines, links. Will take it from there myself to learn. I know risks involved in highvoltage amp and will take necessary precaution.
thanks and regards.
Hiten
Dont want to start new thread so please bear with me. I already have 12AT7 and EL84 tubes, Can anyone answer few questions (Newbie here).
1) I have an old transformer used in valve amps. The secondary leads is showing 360 V. The RH84 amplifier suggests B+ 315V. Will it be ok to use 360v ? Heater supply is OK (6.3v). Any clever way to drop the voltage OR use some of that voltage somewhere usefull to drop it ? Dont want to put heating resistor.
2) We already have 230V Mains power line is there any other option (Like solid state circuit etc. ) to get around 315 directly from mains line. So I can avoid using old transformer ?
3) I also have two tiny chokes with 4A written on it. Size is approximately 2 inches width x 1 inch height) I doubt the marking '4A' are amperes. Probably they are salvaged from old radio. Can I use them in power supply as filters ? Dont have inductance meter.
4) I have read about the RH84 amp and I know original designer Alex Kitic strongly recommends rectifying valve But valve sellers here are demanding Big money for untested old valves. So can I replace it with SS rectifier.
5) A SS powersupply schematic will be great. That way I can avoid transformer, rectifier issues. Probably chokes too ?
6) Also have some (have 3 leads) pushpull output transformer. Can they be used just to get the 'sound taste' of valve sound ? 5K-8K is written on it.
Please give me suggestions, hints, guidelines, links. Will take it from there myself to learn. I know risks involved in highvoltage amp and will take necessary precaution.
thanks and regards.
Hiten
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Don't rectify mains. Other than being potentially dangerous, you'll make the mods grumpy here.
You can use a small choke between the rectifiers and the first cap to shave off some voltage, and this will also decrease the AC current demand on the high voltage winding of your power transformer. You can download the PSUD simulator and start testing the various Hammond chokes available to determine which one might get you the correct power supply voltage. Is your winding 360V with two wires, or is there a center tap?
You can use a small choke between the rectifiers and the first cap to shave off some voltage, and this will also decrease the AC current demand on the high voltage winding of your power transformer. You can download the PSUD simulator and start testing the various Hammond chokes available to determine which one might get you the correct power supply voltage. Is your winding 360V with two wires, or is there a center tap?
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