Hello Stuart,
operation of a KT66 in my circuit does require some design changes. The driver stage also needs a slight modification to accommodate for the larger voltage swing required. Here is a new version of the schematic:
Design notes:
The KT66 is operated at 15W plate dissipation which is well below the recommended maximum of 25W. This should ensure a very long tube life.
This amplifier exhibits an extremly low distortion figure at full output due to the linearity of the KT66. At normal listening levels I would expect a distortion of less than 0.1%.
For rectification I recommend a 5R4 or GZ37. These have considerable advantages over a 5AR4/GZ34.
The heater supply should be elevated to about 50-60V as indicated in order to stay within the heater to cathode voltage rating which is 100V for both tubes. AC heating is preferable.
If you have any further questions I'd be glad to help you.
Best regards
Michael
operation of a KT66 in my circuit does require some design changes. The driver stage also needs a slight modification to accommodate for the larger voltage swing required. Here is a new version of the schematic:
An externally hosted image should be here but it was not working when we last tested it.
Design notes:
The KT66 is operated at 15W plate dissipation which is well below the recommended maximum of 25W. This should ensure a very long tube life.
This amplifier exhibits an extremly low distortion figure at full output due to the linearity of the KT66. At normal listening levels I would expect a distortion of less than 0.1%.
For rectification I recommend a 5R4 or GZ37. These have considerable advantages over a 5AR4/GZ34.
The heater supply should be elevated to about 50-60V as indicated in order to stay within the heater to cathode voltage rating which is 100V for both tubes. AC heating is preferable.
If you have any further questions I'd be glad to help you.
Best regards
Michael
Michael
Very many thanks for the schematic and notes.
This was exactly what I was looking for and looks very interesting..
When I get around to building it I will contact you again.
This will not be for some time as I am under pressure at work installing some new plant at the moment.
Once again many thanks for your prompt and helpfull reply.
STU
PS.
First post on this forum.
Impressed!!
Very many thanks for the schematic and notes.
This was exactly what I was looking for and looks very interesting..
When I get around to building it I will contact you again.
This will not be for some time as I am under pressure at work installing some new plant at the moment.
Once again many thanks for your prompt and helpfull reply.
STU
PS.
First post on this forum.
Impressed!!
DID ANYONE?
Hi to all!
Well, what I would like to know is whether anyone of the interested parties build the RH84, and whether anyone on this thread built any two of the suggested schematics, in order to compare?
I wanted also to add that I liked the dissecting way in which amperex commented on the possible component upgrades. When it comes to EL84, the best sounding is up to you, they all sound quite good, especially for the price. The Ei Yugoslavia is probably the best sounding current production. When it comes to GE, never had the chance to try, but I think they are only one of the good sounding NOS tubes around.
When it comes to exchanging the ECC81/12AT7 for other types, be careful. The 12AX7 will do the trick, but the 12AU7 will not! I personally prefer leaving the ECC81, since there are quite a lot of good NOS tubes sounding quite well -- Telefunkens, to mention one alternative. But, if the need to change something is overwhelming, try 5965 and E180CC -- they do the trick even better than the ECC81 in spite of the lower mu, since their transconductances are even higher.
Regards to all,
Aleksandar
Hi to all!
Well, what I would like to know is whether anyone of the interested parties build the RH84, and whether anyone on this thread built any two of the suggested schematics, in order to compare?
I wanted also to add that I liked the dissecting way in which amperex commented on the possible component upgrades. When it comes to EL84, the best sounding is up to you, they all sound quite good, especially for the price. The Ei Yugoslavia is probably the best sounding current production. When it comes to GE, never had the chance to try, but I think they are only one of the good sounding NOS tubes around.
When it comes to exchanging the ECC81/12AT7 for other types, be careful. The 12AX7 will do the trick, but the 12AU7 will not! I personally prefer leaving the ECC81, since there are quite a lot of good NOS tubes sounding quite well -- Telefunkens, to mention one alternative. But, if the need to change something is overwhelming, try 5965 and E180CC -- they do the trick even better than the ECC81 in spite of the lower mu, since their transconductances are even higher.
Regards to all,
Aleksandar
Try decwares Zen triode. i've build it and it is SWEET. iI don't ever swich it into pentode mode. It's a scrap build. My first one.
this will be my second one
An externally hosted image should be here but it was not working when we last tested it.
this will be my second one
An externally hosted image should be here but it was not working when we last tested it.
Trying to build the RH84 SE
Hello,
After finishing my symasym amp I would like to build a tube amp, quite small, easy and cheap (as most beginners do)
Searching the net I found this thread and the RH84 SE or even the circuit from Tubemaster are quite what I was looking for.
Now I have a problem (or maybe it isn't really one, we will see)
I can't find 5K OT (at affordable price (outside US)) but I can have 5.2K 60mA EL84 core, now is this OK or should i adapt the circuit to maintain the EL84 working point as it is with 5K OT?
Difference might be minor but at only 5W output power the influence might be valuable? That's the question.
By using diodes instead of the 5U4 tube a transformer of 270V AC should be enough to get the 300 DC, how about the current? Are 120mA ok for the power supply or do I better go for 200mA?
I know I could calculate it but as voltage and current values are not all given .....and I am newbie after all and I prefer getting confirmation from the good guys
Thanks
Alan
Hello,
After finishing my symasym amp I would like to build a tube amp, quite small, easy and cheap (as most beginners do)
Searching the net I found this thread and the RH84 SE or even the circuit from Tubemaster are quite what I was looking for.
Now I have a problem (or maybe it isn't really one, we will see)
I can't find 5K OT (at affordable price (outside US)) but I can have 5.2K 60mA EL84 core, now is this OK or should i adapt the circuit to maintain the EL84 working point as it is with 5K OT?
Difference might be minor but at only 5W output power the influence might be valuable? That's the question.
By using diodes instead of the 5U4 tube a transformer of 270V AC should be enough to get the 300 DC, how about the current? Are 120mA ok for the power supply or do I better go for 200mA?
I know I could calculate it but as voltage and current values are not all given .....and I am newbie after all and I prefer getting confirmation from the good guys
Thanks
Alan
Welcome Smila,
A single ended output transformer of 5.2k should be fine ( marginally less power, marginally less distortion IIRC )
270v ac will be give you 378V dc after rectifier. ( x 1.4 ) approx. Loading will reduce this to around 330 - 340V dc. 250V ac would be better if your going to use solid state rectification.
You can model your supplies in Duncan......PSUD2
If you are not going to be bitten by the valve building bug then 100-120ma output from the transformer will be fine. If you later want to build one of the excellent push pull EL84 designs created on this forum then 200ma would be the way to go.....
Brgds Bill
A single ended output transformer of 5.2k should be fine ( marginally less power, marginally less distortion IIRC )
270v ac will be give you 378V dc after rectifier. ( x 1.4 ) approx. Loading will reduce this to around 330 - 340V dc. 250V ac would be better if your going to use solid state rectification.
You can model your supplies in Duncan......PSUD2
If you are not going to be bitten by the valve building bug then 100-120ma output from the transformer will be fine. If you later want to build one of the excellent push pull EL84 designs created on this forum then 200ma would be the way to go.....
Brgds Bill
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RH 84 - Tube Audio ...... RH DESIGN
After a quick refresher look at Mr Kitic's schematic I remembered I used a 7H choke rated at 100ma + in the power supply.
After a quick refresher look at Mr Kitic's schematic I remembered I used a 7H choke rated at 100ma + in the power supply.
Hello Soonerorlater,
If I'll be bitten by the valve bug will surely depend of the result of my build and the tolerance of my wife
I will download the PSUD from DUNCAN and play around with this, Think it might be helpful.
I'll look for a 200mA transformer then (for further upgrades)
What do you think about the RH84SE?
Thank you for your helping hand!
If I'll be bitten by the valve bug will surely depend of the result of my build and the tolerance of my wife
I will download the PSUD from DUNCAN and play around with this, Think it might be helpful.
I'll look for a 200mA transformer then (for further upgrades)
What do you think about the RH84SE?
Thank you for your helping hand!
The RH84 monobloks i have are similarily based on recyled Grundig iron (OPTs closer to 10k than 5k, so i wouldn't worry about 5.2, that is well within production tolerences of a 5k opt), but we didn't skimp too much on passive parts (all Solen film caps in the power supply), they were still dirt cheap (<$150 cash invested) and have performance far in excess of their modest cost (in one comparo they went head-to-head with a set of Audio Note Conquer and held their own). They measure 3.9W.
dave
Hello again,
Sorry but I need to ask (another) stupid question.
Looking at the power supply of the RH84SE it uses a 300-0-300V Transformer.
Can anybody explain me why I would need these 2*300V?
Is it because of the Tube rectifier?
In my head using a 250V Transformer I coud get 250*SQRT2=353V without load, and ~315V under load should get the requested 300Vafter RC.
An EL84 needs max. 48mA (98mA for two of them)
An ECC81 needs about 10mA
So the Transformer I would use is a 250V AC/120mA and 6,3V for the heating.
(by using solid state rectifier)
Now your turn to:
Thanks a lot
Sorry but I need to ask (another) stupid question.
Looking at the power supply of the RH84SE it uses a 300-0-300V Transformer.
Can anybody explain me why I would need these 2*300V?
Is it because of the Tube rectifier?
In my head using a 250V Transformer I coud get 250*SQRT2=353V without load, and ~315V under load should get the requested 300Vafter RC.
An EL84 needs max. 48mA (98mA for two of them)
An ECC81 needs about 10mA
So the Transformer I would use is a 250V AC/120mA and 6,3V for the heating.
(by using solid state rectifier)
Now your turn to:
- Confirm
- Explain me why to use a 25-0-250V type
Thanks a lot
Using a valve rectifier brings down the dc voltage compared with diodes. Also the cap after the rectifier and before the choke can have a big effect on the final B+. Try playing around with the value of this cap in Duncan.
You can use a 250-0-250 Vac centre tapped transformer or you can use a 250-0 Vac without a centre tap. As you say you don't want to use valve rectification then 250-0 Vac transformer without the centre tap might be more suitable. It should be cheaper as it wouldn't have the 5V rectifier valve heater supply built into it.
I haven't found center tapped transformers in PSUD (maybe I should simply use 2 transformers instead (could have thought before)
That's exactly the point.
Thanks for your replies
Alan
Click below the transformer, to highlight both transformer and rectifier(s),
and right click / Change to select Full wave.
Svein.
A longer winded version of above.....
If you hover your mouse over the description at the bottom of the circuit diagram giving the type of rectifier (default is bridge ss IIRC ) and right click, up will come a box labelled "change", left clicking on this will give you more transformer rectifier setups. Choose ss full wave
If you hover your mouse over the description at the bottom of the circuit diagram giving the type of rectifier (default is bridge ss IIRC ) and right click, up will come a box labelled "change", left clicking on this will give you more transformer rectifier setups. Choose ss full wave
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