I'm somewhat aware of the differences in the 10/10Y/vt25/vt25A/vt52/vt62 family. I have a couple that are labelled 10/VT-25 that use thoriated filaments. I'm planning to build a stand-alone preamp with them.
If 3w output is enough, you might consider trying the 10 as an input tube driving the 6N6G that I've been breadboarding. I know you want to use a DHT output, but it might surprise you.
Technically, that wouldn't be a two stage amp since the 6N6G has two triode sections, the first of which is configured as a cathode follower which is directly connected internally to the output section. All biasing is done internally, the cathode pin just goes to ground. It will produce 4.5w and it's very easy to drive, I'm using a choke loaded 26. I haven't tried the 10 but it should also work fine. I just don't want to restrict the only pair I have to use in one particular amp.
Here's an extremely detailed data sheet for the 6B5, which is the original version with a different base.
https://tube-data.com/sheets/201/6/6B5.pdf
It may not be something that you'd want to use in this build, but you might find it interesting anyway. Most of the technical details are over my head but I really like using them. I previously modded a PP 6V6 amp to use them.
I can't comment on the expected life of the HY69 since I have only been using them for three or four months. I would point out that they were used by the military and after WW2 they were intended for use by police, fire, civil defense, etc. So I would expect them to have a reasonable life expectancy since these are critical applications. I would be happy to get the triode plate curves for them and can contribute a tube if that would help. In the end though, I would be very tempted to use them in pentode SE with regulated screen grid and Schade FB.
50AE, you may be a successful practitioner, but you have a lot of confusion about transformer basics.
''I have your sample in hand LG, and if I may impose, would you also consider running the experiment on an HY1269?
minhaj, I have run these tubes a few times, and had no issue with their life. Class A PP of course...''
cheers,
Douglas
''Hi Douglas - I'd be happy to trace both, I'll shoot you my address.''
I am very happy, I remain grateful to both of you. Great people!
So I come to the conclusion that there is no issue with hy69 lifetime.
I wait for hy69 triode curves.
Regards
minhaj, I have run these tubes a few times, and had no issue with their life. Class A PP of course...''
cheers,
Douglas
''Hi Douglas - I'd be happy to trace both, I'll shoot you my address.''
I am very happy, I remain grateful to both of you. Great people!
So I come to the conclusion that there is no issue with hy69 lifetime.
I wait for hy69 triode curves.
Regards
''If 3w output is enough, you might consider trying the 10 as an input tube driving the 6N6G that I've been breadboarding. I know you want to use a DHT output, but it might surprise you.''
I think its difficult cause 10/10Y needs at least 200 volt at its plate @20ma current with 10K load resistor. But B+ for 6N6G is max 300 volt. Any other output tube which is okay with 400 volt and mu of 17-20?
Regards
I think its difficult cause 10/10Y needs at least 200 volt at its plate @20ma current with 10K load resistor. But B+ for 6N6G is max 300 volt. Any other output tube which is okay with 400 volt and mu of 17-20?
Regards
Since it has not been brought up yet, examine type HY51A. From about 600V and zero bias with a 5k load, significant power should be available with a +/- 30V signal.
I am working up a way to run these grounded grid, and biased with an adjustable B+. 10k a-a load, and idling at ~100 mA/tube. Matched tubes will be required, as well as a solid interstage driver TX( 3k:600 and driven by small sweeps, perhaps 6CD6 ). It will NOT be light...heh-heh-heh
cheers,
Douglas
I am working up a way to run these grounded grid, and biased with an adjustable B+. 10k a-a load, and idling at ~100 mA/tube. Matched tubes will be required, as well as a solid interstage driver TX( 3k:600 and driven by small sweeps, perhaps 6CD6 ). It will NOT be light...heh-heh-heh
cheers,
Douglas
Good point. It would be difficult if configured as a conventional amp with a single PS.
Or would it? Probably a dumb question but . . . is there some technical reason why the first (higher voltage) section of a PS can't be used to power the input tubes and the following section (lower voltage) can't be used to power the output tubes? I've never seen it done but I'm not sure if that's simply because most all output tubes require higher voltage and most all input tubes.
If that's not possible, the solution would be to use a modular design, as I believe Andy does with his amps. One section with the output tubes only and one with the 10s. Each with their own PT.
I haven't spent much time on the 10 preamp idea but I was thinking of using ~280v plate, a pair of 9v batteries (-19v) for grid bias, and each tube loaded with a pair of Hammond 156c plate chokes in series, which would allow up to 16mA plate current. This would require a supply voltage of ~390v.
"Or would it? Probably a dumb question but . . . is there some technical reason why the first (higher voltage) section of a PS can't be used to power the input tubes and the following section (lower voltage) can't be used to power the output tubes? I've never seen it done but I'm not sure if that's simply because most all output tubes require higher voltage and most all input tubes."
The driver tube need more filtering your proposed PS will not, I think, support the need.
"each tube loaded with a pair of Hammond 156c plate chokes in series, which would allow up to 16mA plate current."
Are you sure about 16ma current handling?
Regards
The driver tube need more filtering your proposed PS will not, I think, support the need.
"each tube loaded with a pair of Hammond 156c plate chokes in series, which would allow up to 16mA plate current."
Are you sure about 16ma current handling?
Regards
I was only asking if the order of the PS feeds could be reversed. I would assume you could include as much filtering as you thought was necessary before you send the voltage to the input tube.
The Hammond 156c is rated for 8 mA each so two in series should handle 16 mA, correct?
My theory matches my practice very well, on the contrary your previous claims like the turn-to-turn capacitance was extremely wrong.
Edit: For clarification, I'll write describe capacitances from less to more significance. Inside an OPT:
-Turn to turn capacitance: Extremely small, usually neglected
-Primary to primary layer: Can be calculated by the formula Cp = ( Cs * 1.33 x N - 1 / N^2 ) / S, where N is the number of primary layers, Cs is the static capacitance from the contact layer surface area and MLT, and S is the number of primary sections. 1.33 stands for the classical, left to right, right to left winding instead of Z-winding. For the most of the time it can be neglected, can range from 50pF to 200pF
-Primary to secondary: It is the most significant one due to the highest voltage potential difference and within an OPT where we assume the secondary is at zero potential, capacitance can be found by C = ( (Pn - 0.5) / Pa ) ^2 * Cs ; where Pa is the overall number of primary layers and Pn is the target primary layer to be calculated. Pa is max where the anode connection is and decreases towards 1 where the ground potential (B+ connection is). The rule of thumb is, you want to keep the closest to anode layers far away from the secondary layers.
Turn-to-turn capacitance is only significant for a really small number of turns and in practice this is valid for RF coils or SMPS transformers. Mathematically the same law as the primary to primary capacitance applies.
Last edited:
OK, I'm obviously not real familiar with plate chokes. I'm using them for the first time in the 26 - 6N6G SET I have on the breadboard.
So, is there any way to use these (perhaps in parallel) that would allow 16 mA of plate current?
If not, I guess either a different plate choke or a resistor would be necessary.
Thanks for the clarification. So, in parallel, they'll be good for 16 mA with an inductance of 75H.
And, paralleling two chokes will double the capacitance.
(lower load impedance at high frequencies).
(lower load impedance at high frequencies).
I installed 6N6G on a TubeLab SSE board. It's basically a drop in on that board. There is a thread on it down in the TubeLab forum.
6N6G in the low voltage SSE
I do not recall getting 4.5 watts out of one, though ...
Last edited:
It would working, but gain only about 7 and output impedance (without coupling capacitor) near to 5kOhm.
With this gain at 2V RMS the output only 40Vpp.
With this gain at 2V RMS the output only 40Vpp.
I had not come across the 6N6G before, I think it is a fun little tube, I have some suitable transformers, I might breadboard it with a 6.5K load with a pentode input two-stage feedback loop. Plate resistance is high, but I think the output Z could be made acceptable with feedback.
Anyway, I digress. I will post triode curves for HY69 and HY1269 when I have them.
Anyway, I digress. I will post triode curves for HY69 and HY1269 when I have them.
Thanks for posting this. I'm somewhat fascinated with the 6N6G. They're so easy to work with and they only require a 15v input signal, which is nice. They're not very hard to find or expensive either.
The output wattages I posted earlier [Edit: Oops, I think that was a different thread
] for the various tubes were just pulled from their data sheets. I have no way of measuring any of them. I assume they are valid, at least in comparison to each other. They're all in the same ballpark from a practical standpoint, the biggest difference being the need to run the 6V6 and EL84 in pentode to get the same power as the 6N6G triode. I guess their output would be about half in triode. The 26 - 6N6G SET I have on the breadboard seems to put out plenty of power for my use, whatever it actually measures. It sounds great with the DHT input tube. It seems you also liked it even though it you were running it at only 250v in the amp. In my current setup I've got 292v on the plate of the output section and 313v on the input section.
It appears that neither one of us is using an optimal OT. Mine were sourced from a Voice of Music SE 6BQ5 amp and measure 8.8k into 8 ohms. I've got some Edcor GXSE 15w 8k:8 on order, which are slightly closer to the 7k spec in the data sheet.
I also have a modded Magnavox 6V6 console amp that uses them in PP with all the stock transformers. The front end uses 5751s in a circuit copied from a $3500 Leben EL84 amp.
It's a cool tube that is definitely overlooked.
Last edited: