Hi,
To spoil the fun, the circuit Cory shows (part of it) was published in Audio Reality.
While I've read part of that book frowning heavily on some wild unfounded claims the EL509 shouldn't have any trouble running at 700VDC.
These are sweep tubes capable of 8KV pulsed current, remember?
If the tubes are flaky don't blame the circuit I'd say, blame your tube vendor.
For the record, these EL509 adhere to the magnoval standard, NOT noval.
Amongst 9-pinners the most common are noval, magnoval and novar.
The magnoval sockets should be of the ceramic / PTFE type for best HV insulation.
Cory,
Maybe it would be a good idea to subscribe to the Transcendent Audio forum and see what other members' experiences are with this particular circuit.
Cheers,
To spoil the fun, the circuit Cory shows (part of it) was published in Audio Reality.
While I've read part of that book frowning heavily on some wild unfounded claims the EL509 shouldn't have any trouble running at 700VDC.
These are sweep tubes capable of 8KV pulsed current, remember?
If the tubes are flaky don't blame the circuit I'd say, blame your tube vendor.
For the record, these EL509 adhere to the magnoval standard, NOT noval.
Amongst 9-pinners the most common are noval, magnoval and novar.
The magnoval sockets should be of the ceramic / PTFE type for best HV insulation.
Cory,
Maybe it would be a good idea to subscribe to the Transcendent Audio forum and see what other members' experiences are with this particular circuit.
Cheers,
Thanks for the welcome PRR. Like many folks these days, I don't have as much free time as I would like. But, I've been following the posts here for the last couple of weeks and realized that I was learning a lot from many of the posts and that I might make a small contribution from time to time.
As it turns out, I also have Audio Reality, but I didn't recognize the schematic as the Super Compact 150W amp. So I have the values that are specified for the screen regulator. Also, my question about the follower in the first stage has been answered, namely the follower is there because the extra triode section was availalble.
As PRR suggested, Mr. Rozenblit has intentionally used the 4ohm output with 8ohm speakers to bump the primary impedance. With the EL509s, the amp can deliver 150W pretty easily.
Cadman, if you use the EL34 with the 4ohm tap into 8ohms, your power will go up considerably, but you'll still have to rewire the screen regulator.
Thanks for the diagram runeight! Just what I needed Any gotchas on resistor wattages?
I really appreciate everyone chiming in, it's amazing the things you learn. I have no qualms at all about running an 8ohm load on the 4 ohm taps. Unfortunately, my chassis already pretty much finished, but if I find that I simply can't live with just two tubes per channel I might be able to squeeze a couple more in. The reason the EL34 sounds so appealing is that I have a bunch on hand and I dig its sound. If all of that goes according to plan, maybe one day an upgrade to KT90s won't be too bad. I considered those MkIIs but the price per tube is a little rich for my blood and I'm a bit skeptical on the new stuff.
Suggestions welcome!
Any gotchas on resistor wattages?I really appreciate everyone chiming in, it's amazing the things you learn. I have no qualms at all about running an 8ohm load on the 4 ohm taps. Unfortunately, my chassis already pretty much finished, but if I find that I simply can't live with just two tubes per channel I might be able to squeeze a couple more in. The reason the EL34 sounds so appealing is that I have a bunch on hand and I dig its sound. If all of that goes according to plan, maybe one day an upgrade to KT90s won't be too bad. I considered those MkIIs but the price per tube is a little rich for my blood and I'm a bit skeptical on the new stuff.
Suggestions welcome!
You're welcome!
I've reloaded the schematic with resistor power ratings. See the original posting above.
Also, Bruce likes to use 10k grid stoppers so I put that back just so you don't have to rewire it too.
I recommend using three 100V 5W zeners for the reference. This will reduce temperature drift a little and spread out the power dissipation on the zeners, which will also help reduce drift. If you need more stability, you can string six 51v zeners.
Also, I'm running half the current through the sink resistor than what Bruce used (4ma vs 2ma). If you want to stick closer to his design you can replace the 220k 2W resistor with 100K 5W.
And since there will be some variation in the zeners and the tubes, you might consider the adjustable supply with the 50k pot tied to the ground and the 150k resistor between it and the grid. You can bury a slotted shaft pot on the back of the chassis.
Please let us know how it comes out.
I've reloaded the schematic with resistor power ratings. See the original posting above.
Also, Bruce likes to use 10k grid stoppers so I put that back just so you don't have to rewire it too.
I recommend using three 100V 5W zeners for the reference. This will reduce temperature drift a little and spread out the power dissipation on the zeners, which will also help reduce drift. If you need more stability, you can string six 51v zeners.
Also, I'm running half the current through the sink resistor than what Bruce used (4ma vs 2ma). If you want to stick closer to his design you can replace the 220k 2W resistor with 100K 5W.
And since there will be some variation in the zeners and the tubes, you might consider the adjustable supply with the 50k pot tied to the ground and the 150k resistor between it and the grid. You can bury a slotted shaft pot on the back of the chassis.
Please let us know how it comes out.
This widely rumored but not true. EL509 and KT90 are physically and electrically different.
You can look up the data sheets and test and look at the tubes themselves to verify this. They're both good tubes in their own right but not electrical equivalents.
I am not that fond of the Svetlana "EL509" for a few reasons, first, they're really 6P45S, and thus not an exact electrical equivalent (eg: the filament current is 500ma higher than EL509), and the bulbs are shorter and larger diameter than Philips spec for EL509 and thus don't fit in some equipment.
Many of the Yugo EL519/6KG6A we sell go into amatuer radio linear amps and thus get punished much worse than they would
in any audio amplifier...one that was dragged in here had 6 Yugo EL519's with a claimed (I don't believe it) output of 1 KW!
Actually, that's almost spot on what Philips suggested for EL34's wired ultralinear.
See here for a copy of the data sheet
page regarding this:
http://www.triodeel.com/6ca7ap5.gif
Hi,
Not that I want to write history but I happen to know this for a fact, Ned:
First of all, I don't it's all that widely rumoured at all but anyway; the mere fact of rewiring a magnoval into an octal socket will change electrical parameters, no doubt.
This, of course does reflects itself in the datasheets.
Big question is, if someone did design the "new" KT90 then who was it and who order 10.000 of them to fulfill EI's requirements I wonder?
Fact is nobody actually did it on their own and no, the KT90 wasn't a new design, just a resocket job.
Now, if anyone has history to add be my guest...
Not that I want to write history but I happen to know this for a fact, Ned:
First of all, I don't it's all that widely rumoured at all but anyway; the mere fact of rewiring a magnoval into an octal socket will change electrical parameters, no doubt.
This, of course does reflects itself in the datasheets.
Big question is, if someone did design the "new" KT90 then who was it and who order 10.000 of them to fulfill EI's requirements I wonder?
Fact is nobody actually did it on their own and no, the KT90 wasn't a new design, just a resocket job.
Now, if anyone has history to add be my guest...
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