Do you hear any improvement using two VR150 (one for each channel) in place only one shared for both channels?
I should try that, I'll have to rig up another ccs and see If I can squeeze in a heat sink. I probably have a dozen or so VR150 tubes.
There are a couple of issues I found last night that I gotta sort out: The first one is that there is some buzz in the left channel and the CCS voltage on that side seems to be slowly creeping up, it's not the tube because I tried another NOS tube and it did the same thing, If I wrap that side in tin foil the buzz goes away (well quiets down, but still there). The other issue is the ceramic plate cap on one of the 3B28 tubes gets really hot, but the other is cold... Weird
Never mind, I figured it out....I had miswired two grounds. All is well now and the preamp sounds amazing! Oh, I also added a capacitor (.022uf) across the VR tube, which got rid of the small amount of hiss that I was hearing. I isolated the sockets from the chassis and there is not microphonics!! I am very happy with this build and I have already taken apart my other 26 preamps for parts!
Perhaps there is some other alternative 26 and 10Y tube for such a preamp.
It could be the Philips PT8. DHT very close to WE101F.
These are the data:
heater V 4
heater I 0.25 A
anode V 130
grid V -8
anode I 8 mA
transconductance 1.3 mA/V
plate R 5.5K
amplification factor 7 V/V
load resistance 6K
It could be fine with LL1660 / 10mA (ALT Q) or LL2745 (ALT R).
I'd like to know what you think.
It could be the Philips PT8. DHT very close to WE101F.
These are the data:
heater V 4
heater I 0.25 A
anode V 130
grid V -8
anode I 8 mA
transconductance 1.3 mA/V
plate R 5.5K
amplification factor 7 V/V
load resistance 6K
It could be fine with LL1660 / 10mA (ALT Q) or LL2745 (ALT R).
I'd like to know what you think.
Attachments
Thanks for posting, hadn't seen these before. Nickel plate?
I'd have a place for them, are they for sale?.
Nice looking tubes, electrically similar to STC 3A/141A
Load impedance closer to 12k at the lowest usable frequency, much better suited for inductive load than 26 or 01A.
HK
I'd have a place for them, are they for sale?.
Nice looking tubes, electrically similar to STC 3A/141A
Load impedance closer to 12k at the lowest usable frequency, much better suited for inductive load than 26 or 01A.
HK
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I have a couple, and I'm studying what to do with it.
They are tubes born for telephone use and years ago it was easy to find them at a low price.
They were used in the KATELELO amplifier.
Sometimes there is someone who sells them on ebay.
They are tubes born for telephone use and years ago it was easy to find them at a low price.
They were used in the KATELELO amplifier.
Sometimes there is someone who sells them on ebay.
Looks like a good input tube.
I would use a nice 80% nickel plate loading choke, direct couple to the next stage and use the filament current to bias the tube with an unbypassed cathode resistor.
Stacked supplies with the driver biased by plate current through the combined DCR of the plate load of the input tube and some series resistance plate side which would also serve to decouple the capacities of the winding.
Maybe a CCS fed shunt capacitor, this would move all bias shift to the plate of the driver.
Addition to drive impedance would be Rk x 6 which is negligible, overall half that of 26 or 01A.
Nicest looking tube. Do you have a couple of couples, or just a couple?. 🙂
I would use a nice 80% nickel plate loading choke, direct couple to the next stage and use the filament current to bias the tube with an unbypassed cathode resistor.
Stacked supplies with the driver biased by plate current through the combined DCR of the plate load of the input tube and some series resistance plate side which would also serve to decouple the capacities of the winding.
Maybe a CCS fed shunt capacitor, this would move all bias shift to the plate of the driver.
Addition to drive impedance would be Rk x 6 which is negligible, overall half that of 26 or 01A.
Nicest looking tube. Do you have a couple of couples, or just a couple?. 🙂
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These are awesome.
Same voltage gain, same voltage across the tube and filament requirements.
3x the plate current and 1/3 the drive impedance.
Havent seen the transfer curves, but I suspect they're every bit as good.
PT8 input direct coupled to PT26 as a driver to _whatever.
Very similar to 12A and 71A respectively.
Same voltage gain, same voltage across the tube and filament requirements.
3x the plate current and 1/3 the drive impedance.
Havent seen the transfer curves, but I suspect they're every bit as good.
PT8 input direct coupled to PT26 as a driver to _whatever.
Very similar to 12A and 71A respectively.
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Wow just look at what they're asking for in ebay !!!!! Is it really worth the price of admission ?
Probably not: 01A are available at less than 10x that price.
M: no idea.. should be easy enough to research.
M: no idea.. should be easy enough to research.
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The current auction ebay (in USA) is also for a couple of used PT8 ... (!!!)
The others (PT26 or TS26), have never been seen anywhere on sale and there is no technical news. They would have been really unusable without the hand-written data sheet inserted in the tube roll-pack package.
The others (PT26 or TS26), have never been seen anywhere on sale and there is no technical news. They would have been really unusable without the hand-written data sheet inserted in the tube roll-pack package.
Nice tubes but very hard to surpass 01A/12A or 71A.
As to 'really unusable', give them to me 🙂
As to 'really unusable', give them to me 🙂
I would never want to build 3-stage amps.
For 2a3 I think 46 is better as a guide, and if the gain is not enough, just insert a 1: 4 or higher transformer upstream.
(preferably coupled with interstage)
For 2a3 I think 46 is better as a guide, and if the gain is not enough, just insert a 1: 4 or higher transformer upstream.
(preferably coupled with interstage)
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