3)
Power transformer 300‐0‐300 V, 5V@3A, 6,3V@4A (haven’t found anyone affordable yet)
GIVE EDCOR A CALL THEY WILL HAVE WHAT YOU NEED FOR REASONABLE COST. I ODERED MINE (XPWR008) 120V 60HZ 300-0-300@200MA 6.3V@4A . 5.0V@3A FOR $57
4)
Diode 5U4 T-5U4G-CHINA
5)
Choke 20 H min. 50 mA HAMMOND, FILTER CHOKE 20 H, 100 mA, ENCLOSED, (like to find a cheaper option)
I USE HAMMOND 15 H @ 75MA WORKS FINE
Power transformer 300‐0‐300 V, 5V@3A, 6,3V@4A (haven’t found anyone affordable yet)
GIVE EDCOR A CALL THEY WILL HAVE WHAT YOU NEED FOR REASONABLE COST. I ODERED MINE (XPWR008) 120V 60HZ 300-0-300@200MA 6.3V@4A . 5.0V@3A FOR $57
4)
Diode 5U4 T-5U4G-CHINA
5)
Choke 20 H min. 50 mA HAMMOND, FILTER CHOKE 20 H, 100 mA, ENCLOSED, (like to find a cheaper option)
I USE HAMMOND 15 H @ 75MA WORKS FINE
I used a pair of Hammond 125ESEs with my screen driven SE sweep tube amp. The bass and overall articulation are pretty swell for cheap iron. I will admit, though, that I closed the loop including the transformers, which should provide more bass extension (at least, until saturation intervenes).
Re: Re: rh84
Well than I throw in the 6CB6a tube, almost pin compatible with the 6au6 and sounds just as good and costed me 25 eurocent a piece.
I tried both 6au6 and 6CB6 with a regulator consisting of 1 mosfet IRF840, 3 resistors and 3 caps. Regulator (217 volt) also feeds the screen of el84. Rk on el84 is 150R, 269 volt on plate, Ia about 40 mA.
B+ 278 volt, rectified with two solid state diodes (no room for tube rectifier); total of 247 uF in psu. Ra on 6au6 150K and on 6CB6 120K. On both tubes Rg2 220K; Rk 733R. In this way the Ia is about 2,2 mA. Feedbackresistor is 220K.
Great sound. I wonder why i started with cascaded 6sn7/300B in the past, this amp would have been a better introduction.
With the 150K Ra on the 6CB6 I measured 78 volt on the plate and 89 volt on the G2. I suppose this is not right so I changed to 120K and this gave 97 volt on plate and 89 volt on grid 2.
It would be great if someone with more knowledge and measuring/simulating equipment could look into this 6au6/6CB6 RH84 concept. As I said before the ecc81-83 is becoming expensive, and this sounds perhaps better.
Bandersnatch said:
Well than I throw in the 6CB6a tube, almost pin compatible with the 6au6 and sounds just as good and costed me 25 eurocent a piece.
I tried both 6au6 and 6CB6 with a regulator consisting of 1 mosfet IRF840, 3 resistors and 3 caps. Regulator (217 volt) also feeds the screen of el84. Rk on el84 is 150R, 269 volt on plate, Ia about 40 mA.
B+ 278 volt, rectified with two solid state diodes (no room for tube rectifier); total of 247 uF in psu. Ra on 6au6 150K and on 6CB6 120K. On both tubes Rg2 220K; Rk 733R. In this way the Ia is about 2,2 mA. Feedbackresistor is 220K.
Great sound. I wonder why i started with cascaded 6sn7/300B in the past, this amp would have been a better introduction.
With the 150K Ra on the 6CB6 I measured 78 volt on the plate and 89 volt on the G2. I suppose this is not right so I changed to 120K and this gave 97 volt on plate and 89 volt on grid 2.
It would be great if someone with more knowledge and measuring/simulating equipment could look into this 6au6/6CB6 RH84 concept. As I said before the ecc81-83 is becoming expensive, and this sounds perhaps better.
Aaah, that is a pity 🙁
Thanks! Do you still have the 300Bs? I can send you the latest schematics for the 2nd generation RH300B, where the driver is (again) ECC81, if you wish (yes, I have finally prepared that schematics for sending). Just email me...
I seem to recall that you have put the Rfb as 220k? Maybe a lower value would be better?
And, are you using the pentodes in triode mode, or in pentode mode (sorry, I was not reading carefully 🙂 )?
Alex Kitic said:
6CB6 and 6AU6 are used as pentode.
I chose 220K for feedback (plate to plate) because if I go lower the voltage on the plate of the driver tube goes up. I was too lazy to change the whole setup to arrive at lower voltage and using a 100K feedback resistor. After all it sounds fine. I have only one channel at this moment with many clipleads but will build a more permanent stereo amp in a neat but small enclosure.
I will mail you for the schematic.
VictoriaGuy said:
Thanks, I have edited in the document in post 37 so the cathode resistor is a 5 w effect resistor.
PIO = paper in oil?
I read somewhere that it was a good idea to use metal film resistors. According to the writher, metal film resistors were a safe choice “with metal film resistor you can’t go all wrong…”
tim614 said:
That looks like value for money but unfortunately Edcor just have one power transformer made for 240 v 🙁 and that on does just deliver 275 v and not 300 v as required. I think Hammond 372BX (300-0-300 @ 100 ma, 5V CT @ 2A, 6.3V CT @ 3A) suits better even thou it is a bit more expensive (98 USD in sweden).
The OPT will be either Edcore GXSE15-8-5K or Hammond 125ESE depending witch I can get cheaper.
Well now its time to start collecting the parts so I can start to build and not only talking about it 😉
/Fredrik
Forsman said:
PIO- paper in oil, yes. Sorry to talk in 'code'....
Metal film resistors should be fine. I think I read somewhere that using slightly higher power rated resistors than necessary (eg 1 watt) could help keep the noise levels down. They often have longer leads as well, which can be useful.
You should get a few terminal strips and keep them on hand- unless your layout planning is very good you may well need some 'intermediate' solder points. (Don't make connections in 'mid-air' as seen in some diy projects!)
John
Attachments
The partial feedback connection applied to this amp drives down output impedance to very low levels. In my experience this allows two things - the pentode can control small output transformers extremely well so the quoted specks for the Hammond are likely to be far exceeded over normal SE configuration. Secondly these designs seem to be surprisingly tollerant of impedance missmatch on the output transformer, ie its designed for a 5K load, but is more than happy with anything from 3K5 to 7K.
This design approach is a vertitable miracle for producing the goods with whatever you throw at it.
Also as Alex has pointed out, there is no need to regulate the screen or even cap couple it. the amp sound virtually identical whatever you do with your screens. I think the exception to this would be if you are running a Pentode front end (a very good idea for many design reasons), then a screen regulator for the front end would be a very good idea and pathetically simple to implement.
Shoog
This design approach is a vertitable miracle for producing the goods with whatever you throw at it.
Also as Alex has pointed out, there is no need to regulate the screen or even cap couple it. the amp sound virtually identical whatever you do with your screens. I think the exception to this would be if you are running a Pentode front end (a very good idea for many design reasons), then a screen regulator for the front end would be a very good idea and pathetically simple to implement.
Shoog
I'm trying a partial feedback amp with a 6EW6 front end and 6P3CE output, using the Edcor GXSE series iron. Ill be trying an active shunt regulator for cathode bias on the output tube, and approach that worked well with a smaller amp. If it work well, I might try something more ambitious with larger iron.This amp will fit inside a 6" cube, with transformers and guts inside, tubes on top, powered by a switching power supply.
Alex Kitic said:
Hi Alex I am also living in the Netherlands and a tubefan. Reading through this topic I saw that you have developed a 2nd generation RH300B. I am interested in your latest schematics. Is it also possible for me als to receive these schematics from you. Thanks in advantage and keep up the good work. 😀
RH 2nd generation
Yes, audiotube, you can: just email me (find the mailing details on my site)... as I have finally prepared the "official schematics" for RH88 and RH300B.
The 2nd generation RH amps differ from the first in even simpler schematics (less parts, less possibility to make mistakes) and are addressing higher power.
The purpose of the RH88 (for KT88, 6550...) is providing as much power as possible with the RH sound that I (and many audiophiles/diyers) like 🙂
The purpose of the RH300B is the application of the RH principle to the so renowned 300B tubes, improving on the sound of 300B amps in the various details that RH amps provide "better", i.e. bass, control... etc.
I just do not feel like publishing it "just like that" on the forum... so all those interested are welcome to email and ask. Of course, I would like those to be really interested in building the amps, so we can have some "real world" feedback on the RH 2nd generation series.
Regards,
Alex
Yes, audiotube, you can: just email me (find the mailing details on my site)... as I have finally prepared the "official schematics" for RH88 and RH300B.
The 2nd generation RH amps differ from the first in even simpler schematics (less parts, less possibility to make mistakes) and are addressing higher power.
The purpose of the RH88 (for KT88, 6550...) is providing as much power as possible with the RH sound that I (and many audiophiles/diyers) like 🙂
The purpose of the RH300B is the application of the RH principle to the so renowned 300B tubes, improving on the sound of 300B amps in the various details that RH amps provide "better", i.e. bass, control... etc.
I just do not feel like publishing it "just like that" on the forum... so all those interested are welcome to email and ask. Of course, I would like those to be really interested in building the amps, so we can have some "real world" feedback on the RH 2nd generation series.
Regards,
Alex
I've been playing around with this amp a bit trying to tweak it to what sounds good to me within my system. It seems to be a bit too forward in the female vocals and I was wondering if playing with the feedback resistor would help. Overall, it does sound great but like not quite perfect yet. So would decreasing the feedback resistor flatten the peaks? Or should I try maybe a different driver tube, ie a pentode? I'm not much of a designer but more of a tinker'er (if there is such a word). TIA...
Have you considered that it might be showing up a shortfall in your speakers. If so then no amount of tweaking is going to calm those female vocals. A good frequency sweep with a scope and a dummy load will tell you if the amp is the source of the problem, then do the same with your speakers as the load and see if there are any impedance anomalies.
You could spend a lot of time chasing a red herring.
Shoog
You could spend a lot of time chasing a red herring.
Shoog
Perhaps the quality of the OPT can be the issue (?) and sometimes a proces of breaking in new parts within the system can temporarily lead to "unnatural" sound. Black Gates somewhere ?
FORWARDNESS
The amp is generally not a "forward" one, although it does not sound laid back and reproduces a very detailed image. Therefore, if your SYSTEM with this amp sounds forward in the female vocals (mid/upper mid) it just means that it is less muffled and more detailed than your previous amp.
Actually, forwardness is a matter of system and the only reasonable way to cure it, unless you are going to do something very serious with your speakers (or tweak your source, or your preamp -- you have not provided data on those elements), would be some TUBE ROLLING. If you are using a tube rectifier, switching to a warmer and more muffled (like 5AR4/GZ34) might help, as well as a better quality tube complement (a nice Philips E81CC could do the trick instead of a garden variety 12AT7 with very small greyish anode).
Of course, there is not enough data, so please help us help you 🙂
The Rfb resistor should remain as it is, and has nothing to do with the forwardness. It makes the amp work as it works, and changing it to a smaller or larger value will just alter the operation of the amp.
Regards,
Alex
The amp is generally not a "forward" one, although it does not sound laid back and reproduces a very detailed image. Therefore, if your SYSTEM with this amp sounds forward in the female vocals (mid/upper mid) it just means that it is less muffled and more detailed than your previous amp.
Actually, forwardness is a matter of system and the only reasonable way to cure it, unless you are going to do something very serious with your speakers (or tweak your source, or your preamp -- you have not provided data on those elements), would be some TUBE ROLLING. If you are using a tube rectifier, switching to a warmer and more muffled (like 5AR4/GZ34) might help, as well as a better quality tube complement (a nice Philips E81CC could do the trick instead of a garden variety 12AT7 with very small greyish anode).
Of course, there is not enough data, so please help us help you 🙂
The Rfb resistor should remain as it is, and has nothing to do with the forwardness. It makes the amp work as it works, and changing it to a smaller or larger value will just alter the operation of the amp.
Regards,
Alex
more details...
There could be a "synergy" issue with my system and not the amp itself it seems. Could very well be... Here is what I have: preamp is an Aikido with 6CG7/12BH7 >> RH84 (Hammond 125ESE OPT) >> Fostex FE167E in a MLTL. Granted, these aren't the best OPT but this is what I have. Tubes in the amp are also from my junk box and coupling caps are just Orange Drops.
I am using a DC coupled 6EM7 amp as my reference but would like more output power.
I just recently finished building one of those step attenuators with about a 100 resistors attached and tried them in my 6EM7 amp. Without the pre-amp I noticed that the female vocals got a bit tamed and flat sounding. My thought were that the pre-amp was adding some color to the system that I liked and that without it things got bland. Perhaps I should try hooking this attenuator to the RH84 without the pre-amp and see what happens. Maybe this would tame some of the upper registers.
I like this amp very much and if I could get this last 2% I would be a happy camper. I'm thinking about getting some new OPT also. Then I could stick this amp in a nice chassis instead of my butt ugly breadboard and use it as my living room amp. Planning these things are so much fun...
There could be a "synergy" issue with my system and not the amp itself it seems. Could very well be... Here is what I have: preamp is an Aikido with 6CG7/12BH7 >> RH84 (Hammond 125ESE OPT) >> Fostex FE167E in a MLTL. Granted, these aren't the best OPT but this is what I have. Tubes in the amp are also from my junk box and coupling caps are just Orange Drops.
I am using a DC coupled 6EM7 amp as my reference but would like more output power.
I just recently finished building one of those step attenuators with about a 100 resistors attached and tried them in my 6EM7 amp. Without the pre-amp I noticed that the female vocals got a bit tamed and flat sounding. My thought were that the pre-amp was adding some color to the system that I liked and that without it things got bland. Perhaps I should try hooking this attenuator to the RH84 without the pre-amp and see what happens. Maybe this would tame some of the upper registers.
I like this amp very much and if I could get this last 2% I would be a happy camper. I'm thinking about getting some new OPT also. Then I could stick this amp in a nice chassis instead of my butt ugly breadboard and use it as my living room amp. Planning these things are so much fun...
Re: more details...
It wouldn't be an impedance peak in the speakers pushing the sound forward thou... the 167 is kinda forward naturally thou (in stock state anyway).
dave
RockysDad said:
It wouldn't be an impedance peak in the speakers pushing the sound forward thou... the 167 is kinda forward naturally thou (in stock state anyway).
dave
Full range speaker setups can be a bit peaky on the upper midrange. Infact I have much the same issue myself. It can be an on axis issue associated with beaming from the sharp cone profile of the driver. It can be an artifact of the baffle suddenly disappearing. It can be an issue with the back wave reinforcing front wave at a critical point - in this case it is likely that there will be dips either side of the peak making it sound even worse.
Unfortunately the better the amp the more you are likely to notice these artifacts of your speakers.
Shoog
Unfortunately the better the amp the more you are likely to notice these artifacts of your speakers.
Shoog
Re: more details...
i too have fostex backload horn and heresy. the fostex did not sound good to me compared to my heresy the fostex sound nasal and not as detail.
opt is also the key parts to upgrade that makes the bigest diferent, i had the rh with cheapie EDCOR and then upgraded to TRANSCENDAR and it was night and day.
RockysDad said:
i too have fostex backload horn and heresy. the fostex did not sound good to me compared to my heresy the fostex sound nasal and not as detail.
opt is also the key parts to upgrade that makes the bigest diferent, i had the rh with cheapie EDCOR and then upgraded to TRANSCENDAR and it was night and day.
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