Hi, as the newbie I am I would appreciate some advice on building my first amplifier. I’ve been reading, both on this forum and in other texts recommended on this site, and found that the RH84 amplifier has a very good reputation and seams fairly easy to build for a first timer.
There are pretty many things things that I have problem with comprehending and one is how to choose the output transformer. What is important when it comes to choosing OPT? As far as I understand (that goes for all this text) there are a couple of criteria that need to be met and some that doesn’t. For me it need to be affordable, I don’t have the budget to purchase the best one on the market so my question is witch gives me most value for money without ruin me?
The impedance of the OPT should be 5 KΩ, according to the drawing. That is easy to find but how is it with the current it is designed for. Claus Byrith states in his article on building up on Lundahl transformers that one should choose an OPT designed for the right current for it to operate at its best. I’ve been looking at Hammond’s OPT´s but I can’t find any current marking. Do I need to pay attention to this or is it subsequent to sound quality? On the other hand I don’t knew what the current over the OPT is in the RH84 and I’m not skilled to calculate it either (yet
).
As I’m planning to use this Amp with a pair of back loaded full range horns (Ron Clarke´s Austin 166) I guess that the frequency response is of importance. The speakers rolls off at approximately 40 hz (have I read somewhere) and I want the Amp to mach that. With the Hammond 125SE-serie OPT the frequency response is stated to 100-15 000 hz. Is this OPT suitable for the task at all? Can I tweak it to go full range or should I choose from a different series of OPT´s? The Hammond 125ESE caught my eye on the Boozhoundlabs site but in a different amplifier with different tubes (6V6GT).
/Fredrik
There are pretty many things things that I have problem with comprehending and one is how to choose the output transformer. What is important when it comes to choosing OPT? As far as I understand (that goes for all this text) there are a couple of criteria that need to be met and some that doesn’t. For me it need to be affordable, I don’t have the budget to purchase the best one on the market so my question is witch gives me most value for money without ruin me?
The impedance of the OPT should be 5 KΩ, according to the drawing. That is easy to find but how is it with the current it is designed for. Claus Byrith states in his article on building up on Lundahl transformers that one should choose an OPT designed for the right current for it to operate at its best. I’ve been looking at Hammond’s OPT´s but I can’t find any current marking. Do I need to pay attention to this or is it subsequent to sound quality? On the other hand I don’t knew what the current over the OPT is in the RH84 and I’m not skilled to calculate it either (yet
).As I’m planning to use this Amp with a pair of back loaded full range horns (Ron Clarke´s Austin 166) I guess that the frequency response is of importance. The speakers rolls off at approximately 40 hz (have I read somewhere) and I want the Amp to mach that. With the Hammond 125SE-serie OPT the frequency response is stated to 100-15 000 hz. Is this OPT suitable for the task at all? Can I tweak it to go full range or should I choose from a different series of OPT´s? The Hammond 125ESE caught my eye on the Boozhoundlabs site but in a different amplifier with different tubes (6V6GT).
/Fredrik
any single ended output transformer rated for at least 50ma. should do just fine.
i have built six versions of this circuit with salvaged parts using everything from an akai reel-to-reel, zenith s.e. console amps, magnavox, rca consoles. ive used the edcor gxse-15-8k (rated 75ma.d.c.) and it sounds great! the akai was a real gem with two pairs of great power and output transformers of high quality.
i use these amps with some fostex ff225k and theres plenty of power.
very nice circuit, cheers to mr. kitic for sharing with us!
i have built six versions of this circuit with salvaged parts using everything from an akai reel-to-reel, zenith s.e. console amps, magnavox, rca consoles. ive used the edcor gxse-15-8k (rated 75ma.d.c.) and it sounds great! the akai was a real gem with two pairs of great power and output transformers of high quality.
i use these amps with some fostex ff225k and theres plenty of power.
very nice circuit, cheers to mr. kitic for sharing with us!
For a single ended EL84 amp, assuming budget is the most important criteria, I'd make sure the output transformer matches specs on the primary impedance and the intended output load. In your case, if the schematic says 5k ohms and your speakers are an "8 ohm" load, then buy a set of transformers specified for 5k:8 usage. Also make sure the transformers are intended for single ended usage, and that they have an air gap to minimize the effects of core saturation. Beyond that, go for the heaviest transformers you are comfortable affording. They'll have more iron and copper in them, and will have better low frequency extension than smaller outputs.
For new i'd pick Edcor over Hammond. I also wouldn't be afraid to look on eBay for some vintage iron... we've had good luck with German consoles, Nordmende (they have big ones & little ones -- for a FR amp you need the big ones) Grundig, Lowe-Opta. Some of these will reflect more than 5k, that is OK.
dave
dave
I built one with 125ESE's. Works fine. I was so impressed with it that I rebuilt the amp on a proper chassis with better components and Lundahl opt's, I don't remember the model but they are 5K primary with a single 5 ohm secondary (I think). That was a few years ago. I still have not finished it
Someday...
Someday...
transcendar
i also have built the rh84 with great result using edcor ($20 opt)
but when i upgrade to the transcendar it was night and day.
so if i was to built another one transcendar is a great deal, you can get them on ebay for about 115 a pair. edcor for $20 is a great deal sounded decent but i would highly recomend buying
better OPT for great result, after all OPT is the heart of the amp.
i also have built the rh84 with great result using edcor ($20 opt)
but when i upgrade to the transcendar it was night and day.
so if i was to built another one transcendar is a great deal, you can get them on ebay for about 115 a pair. edcor for $20 is a great deal sounded decent but i would highly recomend buying
better OPT for great result, after all OPT is the heart of the amp.
Thank you all for the advice. I´ve read a lot of your earlier posts and many times the level of the discussion is above my level of comprehension. I’m very happy that you all make an effort to answer these kind of elementary questions as well
I´m going to look for some “vintage iron” on ebay (if pick up a couple more phrases I can fool people I know what I´m talking about ). And as long as the impedance is 5k (or slightly higher) and the output is 8 ohm I should choose the heaviest I can afford. But, I probably end up with some of the smaller Edcor. The shipping cost from the US is similar to the cost of the transformer itself so I will try to find something here in Sweden if possible. Saw some OPT on ebay that seemed nice yesterday, all in US or Hong Kong…
It is little hard to find information on what kind of components to prefer. I´ve learned that there are endless variations on resistors and capacitors with the same ratings but different audible character. For capacitors people seems to hail the paper in oil ones. Pretty expensive though.
I´m doing a draft for the parts list, so I know what to shop. Have googled for it but haven´t found any.
Revintidge - Do you think I should turn my eyes to the 6B4G SE amp instead? Is this the Amp you are referring to? Seems to be a little bit more complicated.
/Fredrik
I´m going to look for some “vintage iron” on ebay (if pick up a couple more phrases I can fool people I know what I´m talking about
). And as long as the impedance is 5k (or slightly higher) and the output is 8 ohm I should choose the heaviest I can afford. But, I probably end up with some of the smaller Edcor. The shipping cost from the US is similar to the cost of the transformer itself so I will try to find something here in Sweden if possible. Saw some OPT on ebay that seemed nice yesterday, all in US or Hong Kong…It is little hard to find information on what kind of components to prefer. I´ve learned that there are endless variations on resistors and capacitors with the same ratings but different audible character. For capacitors people seems to hail the paper in oil ones. Pretty expensive though.
I´m doing a draft for the parts list, so I know what to shop. Have googled for it but haven´t found any.
revintage said:
Revintidge - Do you think I should turn my eyes to the 6B4G SE amp instead? Is this the Amp you are referring to? Seems to be a little bit more complicated.
/Fredrik
TRANSFORMERS
The amps was really designed for the first time builder, to provide results even with salvaged parts or the cheapest possible At the time I designed it I was practically penniless and frankly it was a miracle we had to eat and survived the period.
Therefore, the "original" RH84 transformers are "salvaged" units from old Ei radio receivers (yes, the Ei that used to make tubes) that were originally ment to work with an SE EL84 circuit. I used to buy those for peanuts, salvage the transformers and drop the rest. Once I had several, I could "pair" transformers to build amps.
On the other hand, the better transformer you use, the better will the sonic result be, it as simple as that. It extends to the type and quality of all the other parts of the amp you are building, from wire and resistors to caps and tubes... If built with top-notch parts, this amp will give you much more than you dared hope initially from such a common and inexpensive tube complement.
The amps was really designed for the first time builder, to provide results even with salvaged parts or the cheapest possible
At the time I designed it I was practically penniless and frankly it was a miracle we had to eat and survived the period.Therefore, the "original" RH84 transformers are "salvaged" units from old Ei radio receivers (yes, the Ei that used to make tubes) that were originally ment to work with an SE EL84 circuit. I used to buy those for peanuts, salvage the transformers and drop the rest. Once I had several, I could "pair" transformers to build amps.
On the other hand, the better transformer you use, the better will the sonic result be, it as simple as that. It extends to the type and quality of all the other parts of the amp you are building, from wire and resistors to caps and tubes... If built with top-notch parts, this amp will give you much more than you dared hope initially from such a common and inexpensive tube complement.
No, that one I would never recommend
. A 6B4G SE will not need to have more components than the RH84 except for four schottkys and a cap for DC-heating. The five components will easily be soldered directly to the octal socket. You will need a power transformer with two separate 6,3V windings.AMPLIFIERS
What does "the real thing" mean? SE triodes? Without negative feedback?
As a matter of fact, I use as well a 6B4G amp that I obviously designed myself, although there was not much to design except to choose operating points, topology, and power supply. The amp sounds well indeed -- but it does lack power when compared to any of the RH amps (at 2.5W that comes as no surprise). Of course, it does also lack the bass when compared... and it does have lots of hum (AC direct heated on 6.3V) particularly when compared to indirect heated amps like the RH84. Yes, it is well designed and built and it has a respectable power supply, therefore the vocals (singers) are just what you would expect from DHT SE. It is a matter of taste, as well... but it is slightly more complicated to build, due to the separate heaters for each tube (one for the drivers and one for each output tube, I used a 6SN7 to drive two 6B4G).
If it were with 2A3 (lower heating voltage) it would have much less hum. Some would object that DC heating would be better... that is obviously a matter of choice in design, I choose AC for some reasons, obviously.
BTW, my 6B4G are excellent black anode types
The point here is that since one pays much more for DHT the same individual will be prepared to pay much more all the other parts, transformers in particular. In the end, all those other parts will contribute to a sound quality not found in a humble pentode amp which has only an interesting topology to show for itself. But, build the humble amp with the same expensive parts as you would use for the DHT amp, and the results will astonish you. Anyway, since my circuit foresees the 6B4G to work at 300V anode to cathode but approx. 50mA of anode current and 5kOhm anode load, I have built it with the same transformers (Ei salvage) so I had an immediate chance for comparison
What does "the real thing" mean? SE triodes? Without negative feedback?
As a matter of fact, I use as well a 6B4G amp that I obviously designed myself, although there was not much to design except to choose operating points, topology, and power supply. The amp sounds well indeed -- but it does lack power when compared to any of the RH amps (at 2.5W that comes as no surprise). Of course, it does also lack the bass when compared... and it does have lots of hum (AC direct heated on 6.3V) particularly when compared to indirect heated amps like the RH84. Yes, it is well designed and built and it has a respectable power supply, therefore the vocals (singers) are just what you would expect from DHT SE. It is a matter of taste, as well... but it is slightly more complicated to build, due to the separate heaters for each tube (one for the drivers and one for each output tube, I used a 6SN7 to drive two 6B4G).
If it were with 2A3 (lower heating voltage) it would have much less hum. Some would object that DC heating would be better... that is obviously a matter of choice in design, I choose AC for some reasons, obviously.
BTW, my 6B4G are excellent black anode types
The point here is that since one pays much more for DHT the same individual will be prepared to pay much more all the other parts, transformers in particular. In the end, all those other parts will contribute to a sound quality not found in a humble pentode amp which has only an interesting topology to show for itself. But, build the humble amp with the same expensive parts as you would use for the DHT amp, and the results will astonish you. Anyway, since my circuit foresees the 6B4G to work at 300V anode to cathode but approx. 50mA of anode current and 5kOhm anode load, I have built it with the same transformers (Ei salvage) so I had an immediate chance for comparison
Compare what , apples and pears? The 6B4G/2A3 should be loaded with ca 2,5k at 60mA when using a B+ of 300V to sound at its best.
If you carefully read my last post you will see that I talk about DC heating. It is also nonsense that 3 heater are needed. The drivers will have no problems being fed by the 6B4G heater-windings.
The part cost will only differ by the cost of output tubes, a 6S4S is ca 20USD while EL84 is ca 5USD at ebay. Forgot to mention the extreme cost of the schottkys and cap
. So OK, it will be much more expensive with "the real thing", a total of ca 35USD . But you can save few bucks by dumping the rectifier tube and choke if you are on a budget.Fredrik,
Check the ongoing 6B4G/2A3 threads at www.hififorum.nu. Lots of useful information in our own language.
ha, ha, ha!
Says who? And, 300V is a little bit too much, depending on what you loose thru the primary of the OT and thru the cathode resistor... you meant 250V anode to cathode and 60mA, probably, like they used to do in the heyday of audio... did you ever try 300V and 50mA and higher anode load? Ever heard of what higher anode load gives you when compared to lower anode load (i.e. 2.5k with more current and less voltage vs. 5k with less current and more voltage)?
And if you carefully read mine, you would have seen that I WROTE (i could not hear you talking, but could read what you wrote) that it is a desing choice. Unlike you I make my own design choices, I do not let others do that for me
Since I am doing it with AC on the heaters, connecting the left channel and the right channel tube together would have a strange effect (crosstalk), would it not? I'll leave that to you.
On the other hand, the drivers might not have that problem, since they are indirectly heated... but I do not trust insulation that much, we are talking about audiophilia and diy, not ARC cheapskates and the like. I'll happily leave that solution to you as well.
I was not talking about 6S4S, but about 6B4G, eventually Zenith with black anodes. Maybe to you that is the same, to me it is not. When it comes to EL84 there are expensive tubes to be found, not all cost 5 USD.
I'll leave that to you as well. I prefer tube rectifiers.
Come on, get a life! The guy likes it better in English And he likes the RH84 
Maybe you would like it more if you werent so full of... yourself!
Vanity killed the cat, not curiosity...
Says who? And, 300V is a little bit too much, depending on what you loose thru the primary of the OT and thru the cathode resistor... you meant 250V anode to cathode and 60mA, probably, like they used to do in the heyday of audio... did you ever try 300V and 50mA and higher anode load? Ever heard of what higher anode load gives you when compared to lower anode load (i.e. 2.5k with more current and less voltage vs. 5k with less current and more voltage)?
And if you carefully read mine, you would have seen that I WROTE (i could not hear you talking, but could read what you wrote) that it is a desing choice. Unlike you I make my own design choices, I do not let others do that for me
Since I am doing it with AC on the heaters, connecting the left channel and the right channel tube together would have a strange effect (crosstalk), would it not? I'll leave that to you.
On the other hand, the drivers might not have that problem, since they are indirectly heated... but I do not trust insulation that much, we are talking about audiophilia and diy, not ARC cheapskates and the like. I'll happily leave that solution to you as well.
I was not talking about 6S4S, but about 6B4G, eventually Zenith with black anodes. Maybe to you that is the same, to me it is not. When it comes to EL84 there are expensive tubes to be found, not all cost 5 USD.
I'll leave that to you as well. I prefer tube rectifiers.
Come on, get a life!
The guy likes it better in English And he likes the RH84 Maybe you would like it more if you werent so full of... yourself!Vanity killed the cat, not curiosity...
rh84
Fredrick, since you are in sweden, have you considered lundahl iron? I have a RH84 using lundahl iron, and it is very nice. I used 5500 to 5.5 gapped for 50 ma (I think ll1682). As an aside, I have built 4 different rh84 amps, each using different iron, and all sounded excellent. My first used hammond 125ese, the next used ll1682 lundahl, then a parafeed using a 125ese as a plate choke and a hammond 1615 as output, and lastly a version using one -electron output transformer. The ones using lundahl and the one- electron are keepers. I also have SE 2a3, 300b, and pushpull 2a3 and 300b amps for comparison. The 84's hold their own against the other se amps. There are differences sonically between the amps, any of them would be a good choice for my only amp, however the 84's offer the advantage of low cost tubes, which makes rolling for different sounds much more feasible, and they are very quiet - I can put my ears next to the speaker (604 coax)and hear nothing. If you build these amps using nice parts, they will hold their own against about any amp in the same power class.
Jim
Fredrick, since you are in sweden, have you considered lundahl iron? I have a RH84 using lundahl iron, and it is very nice. I used 5500 to 5.5 gapped for 50 ma (I think ll1682). As an aside, I have built 4 different rh84 amps, each using different iron, and all sounded excellent. My first used hammond 125ese, the next used ll1682 lundahl, then a parafeed using a 125ese as a plate choke and a hammond 1615 as output, and lastly a version using one -electron output transformer. The ones using lundahl and the one- electron are keepers. I also have SE 2a3, 300b, and pushpull 2a3 and 300b amps for comparison. The 84's hold their own against the other se amps. There are differences sonically between the amps, any of them would be a good choice for my only amp, however the 84's offer the advantage of low cost tubes, which makes rolling for different sounds much more feasible, and they are very quiet - I can put my ears next to the speaker (604 coax)and hear nothing. If you build these amps using nice parts, they will hold their own against about any amp in the same power class.
Jim
Dear JimW,
I could not have put it better myself, thank you for giving a synthesys of what audiophiles have commented in the last several years since the amp was published and various diyers have built it all over the world.
I am very happy that I have achieved something with tubes and that my ideas steered others towards happyness with their hobby and their crafting skills.
I hope the new series of amps will ripe the same success once diyers start making it!
I am a bit sad though that I was not fortunate enough to live in the States or Canada where I could have made this hobby/interest of mine into a source of revenue allowing me to earn from what I like to do instead of earning from what I know how to do well.
Regards,
Alex
I could not have put it better myself, thank you for giving a synthesys of what audiophiles have commented in the last several years since the amp was published and various diyers have built it all over the world.
I am very happy that I have achieved something with tubes and that my ideas steered others towards happyness with their hobby and their crafting skills.
I hope the new series of amps will ripe the same success once diyers start making it!
I am a bit sad though that I was not fortunate enough to live in the States or Canada where I could have made this hobby/interest of mine into a source of revenue allowing me to earn from what I like to do instead of earning from what I know how to do well.
Regards,
Alex
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