Hi Gents (and ladies).
Please be gentle I'm new here and it's my first post.
I have collected a set of output transformers and a mains transformer suitable to build a push pull power amp using either ECL82 or ECL86 types. As I need to use a separate heater transformer, I can have the option of using PCL/UCL82 and PCL86 which could be a potential saving as these old tv valves seem plentiful in NOS form.
The mains transformer is rated at 240-0-240V x 150mA secondary and 6.3V x 1A which I could use to fire up an EZ81(6CA4) rectifier, or use as heater source for a preamp valve if used and silicon rectifiers.
The output transformers are Radiospares (UK) "Hygrade" devices and are 8k centre tapped (4-0-4k) and the transformer is rated at 60mA, I assume that's 60mA through each 4k winding which will give me plenty of headroom, hell I could possibly use EL84 in push pull!
I'd Ideally like a design that used just the pair of ECL8* per channel, maybe with a concertina phase splitter. I have seen designs using a long tail pair and no preamp valve but it's a bit insensitive at 800mV and I'd prefer around 400 to 500 mV but would be ok as low as 250mV. The Mullard designs are too sensitive at 100mA and I'd be attenuating sources too much I feel.
I hope thats enough information to go on and I'll be grateful for any info and tips.
I have a bit of experience and recently built a SE EL84 amp based on Alex Kitic's RH84 design which was very successful and amazingly completely hum free, no mean feat on an SE amp.
thanks in advance.
Andy.
Please be gentle I'm new here and it's my first post.
I have collected a set of output transformers and a mains transformer suitable to build a push pull power amp using either ECL82 or ECL86 types. As I need to use a separate heater transformer, I can have the option of using PCL/UCL82 and PCL86 which could be a potential saving as these old tv valves seem plentiful in NOS form.
The mains transformer is rated at 240-0-240V x 150mA secondary and 6.3V x 1A which I could use to fire up an EZ81(6CA4) rectifier, or use as heater source for a preamp valve if used and silicon rectifiers.
The output transformers are Radiospares (UK) "Hygrade" devices and are 8k centre tapped (4-0-4k) and the transformer is rated at 60mA, I assume that's 60mA through each 4k winding which will give me plenty of headroom, hell I could possibly use EL84 in push pull!
I'd Ideally like a design that used just the pair of ECL8* per channel, maybe with a concertina phase splitter. I have seen designs using a long tail pair and no preamp valve but it's a bit insensitive at 800mV and I'd prefer around 400 to 500 mV but would be ok as low as 250mV. The Mullard designs are too sensitive at 100mA and I'd be attenuating sources too much I feel.
I hope thats enough information to go on and I'll be grateful for any info and tips.
I have a bit of experience and recently built a SE EL84 amp based on Alex Kitic's RH84 design which was very successful and amazingly completely hum free, no mean feat on an SE amp.
thanks in advance.
Andy.
This is what I'd do with it.
Sensitivity seems to be ok, full power at about 150mV in.
A balanced amplifier will have absolutely no B+ (or B-) hum. PSU design is not paramount, although I would still use a simple two MOSFET regulator.
Use IRF820 MOSFETs or what you have available.
Sensitivity seems to be ok, full power at about 150mV in.
A balanced amplifier will have absolutely no B+ (or B-) hum. PSU design is not paramount, although I would still use a simple two MOSFET regulator.
Use IRF820 MOSFETs or what you have available.
Attachments
Andy,
Go with the 6BM8 or its alternate heater voltage siblings. They are much easier to source than the 6GW8 and its close relations.
If you decide on SS B+ rectification, use 1200 PIV/2 A. Schottky diodes made by Cree. There are no reverse recovery spikes, when Schottkys are employed.
Round the schematic for the ASL AV-8 up. It's exactly what you have in mind.
Go with the 6BM8 or its alternate heater voltage siblings. They are much easier to source than the 6GW8 and its close relations.
If you decide on SS B+ rectification, use 1200 PIV/2 A. Schottky diodes made by Cree. There are no reverse recovery spikes, when Schottkys are employed.
Round the schematic for the ASL AV-8 up. It's exactly what you have in mind.
Mr Curwen, thanks for the circuit but its not what I had in mind, with all those CCS etc.
Eli, I take your point on 6GW8, being European I will say ECL86! If I used that "toob" Then I'd use the PCL86 which is fairly plentiful being an old TV valve and its no problem for the odd heater voltage as I need to use a separate transformer for the filaments. I reckon I might even get away with a 12V AC transformer as the PCL86 seems to need 13.3V and although its a bit on the low side, I'd bet I was getting close enough especially as the UK mains tends to be nearer 250V than 230V. Of course I could go DC and feed them from a 300mA Current source. I would prefer an EZ81 rectifier but as you say there are solid state alternatives. A couple of UF5408 or some schottkies if feeling flush, I have had good results with my KT88 amp by snubbing the rectifiers with .022uF polywotsit capacitors.
Whats this ASL AV-8?
Andy
Eli, I take your point on 6GW8, being European I will say ECL86! If I used that "toob" Then I'd use the PCL86 which is fairly plentiful being an old TV valve and its no problem for the odd heater voltage as I need to use a separate transformer for the filaments. I reckon I might even get away with a 12V AC transformer as the PCL86 seems to need 13.3V and although its a bit on the low side, I'd bet I was getting close enough especially as the UK mains tends to be nearer 250V than 230V. Of course I could go DC and feed them from a 300mA Current source. I would prefer an EZ81 rectifier but as you say there are solid state alternatives. A couple of UF5408 or some schottkies if feeling flush, I have had good results with my KT88 amp by snubbing the rectifiers with .022uF polywotsit capacitors.
Whats this ASL AV-8?
Andy
For AV-8 info., try Wave AV-8 Info. The link may be dead. Should that be the case, try the Way Back Machine.
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The RS "hygrade" output transformers are pretty good. I have a couple of them but have not built anything using them as they seem to be worth a fair few quid to the Marshall 18W guitar amp crowd.
You could certainly use the E/PCL86 with them but how about thinking out of the box a bit and using something like a single TT15? Or an 832/GU32?
Cheers
Matt.
You could certainly use the E/PCL86 with them but how about thinking out of the box a bit and using something like a single TT15? Or an 832/GU32?
Cheers
Matt.
I built this with the 6F3 Chinese tube which is very similar to the ECL85/6F5P/6GV8. The CCS on the output tubes are there only for the toroidal output transformers, you can use simpler cathode bias to your desired level. http://www.diyaudio.com/forums/instruments-amps/253152-4x6gv8-proposed-build-2.html#post3869864
Similarly, you could omit two of the tubes and one of the tube channels. I know you are probably looking at hifi designs and that thread is on the instrument forums, but after building this amp I realise that's what I got out of it, very clean all the way to the edge of hell.
I ended up with a -16V bias, and the tubes are run in pentode mode (not triode as in the schematic) with a regulated screen supply at ~190V. B+ is 210V, and the tubes have 50mA (25mA per tube) of idle current through them. I get about 10W out of this thing and it is pretty loud and clean for what it is.
There is also a link there for a Japanese design using the same tubes, but the first stage is a LTP phase splitter. Both would be quite simple to tweak to the 82 or 86.
Similarly, you could omit two of the tubes and one of the tube channels. I know you are probably looking at hifi designs and that thread is on the instrument forums, but after building this amp I realise that's what I got out of it, very clean all the way to the edge of hell.
I ended up with a -16V bias, and the tubes are run in pentode mode (not triode as in the schematic) with a regulated screen supply at ~190V. B+ is 210V, and the tubes have 50mA (25mA per tube) of idle current through them. I get about 10W out of this thing and it is pretty loud and clean for what it is.
There is also a link there for a Japanese design using the same tubes, but the first stage is a LTP phase splitter. Both would be quite simple to tweak to the 82 or 86.
It doesn't Matt, I think someone may have misread my first post. Ideally somewhere between 250mV and 500mV would work, this because the FM tuner only outputs about 250mV, The DAC (Rega DAC) and disc stage are good for around 1 to 2V.
I have a design in the files based on a LTP phase splitter and no preamp valve which is sensitive to 850mV. It's the old World Audio Designs KECL82 kit amp. I think it would be ok too and as I'd have to build it as a pentode rather than UL It probably would push out a bit more power.
I'm not that interested in complicated CCS etc, I want to keep things as simple as possible. The only thing I may do is adapt Alex Kitics idea for a CCS on the cathode using an LM317 and a single resistor, it's elegant and it works. I built his SE design RH84 and I am listening to it as I type.
That other circuit kind of worries me as I calculated from the published figures that each ECL82 would be pulling 60mA............... thats too much for an EL84 so goodness knows how long an ECL82 would last before giving up at that sort of punishment. 30 to 32mA seems to be a more acceptable cathode current from what I have seen.
Andy.
Just a quick one, the PCL86 is rated at 13.3V x 300mA.
Now I reckon running it at 12V would be about 10% underrated but I feel it would still work fine. also my 12V transformers are nominally 230V secondaries and the local mains is usually between 240 and 250V.
Anyone see why I shouldnt try it?
Now I reckon running it at 12V would be about 10% underrated but I feel it would still work fine. also my 12V transformers are nominally 230V secondaries and the local mains is usually between 240 and 250V.
Anyone see why I shouldnt try it?
I respect the fact that you don't want to have CCSs and such in the audio circuit, but I would advise running that PCL86 heater with a 300mA CCS. They were designed for a specific current not voltage.
Also this gives a softer turn on and significantly lenghtens tube life. No worries on hum either.
Also this gives a softer turn on and significantly lenghtens tube life. No worries on hum either.
The father of Baby Huey:
Push Pull ECL86/6GW8
If you really hate CCS (why ?) it may be substitued for a 220K resistor tied to -220V supply able to deliver a single milliamp
Yves.
Push Pull ECL86/6GW8
If you really hate CCS (why ?) it may be substitued for a 220K resistor tied to -220V supply able to deliver a single milliamp
Yves.
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