I have this idea of using an input transformer as a phase-splitter in a PP 6B4G/2a3. So I would like to know if there are any relatively low mu triodes that could go between the input transformer and the output tubes. For reasons too embarassing to go into my input transformer has to be used at 1:4 or 1:8. Any suggestions would be greatly appreciated🙂
56, it has 2.5 V heater, same as 2A3; mu of about 14 and Rp of 10 k at 5 ma. Well suited for a typical interstage transformer.
Another suggestion is 57, triode-connected; mu of 20, Rp about 11 k at 6 ma.
There are also 6.3 V and octal versions of these tubes (76, 6P5G, 6J7G, 6C6) if you are using 6A3 or 6B4G.
Another suggestion is 57, triode-connected; mu of 20, Rp about 11 k at 6 ma.
There are also 6.3 V and octal versions of these tubes (76, 6P5G, 6J7G, 6C6) if you are using 6A3 or 6B4G.
The plate resistance, rp, of a triode increases by this factor:
u x cathode bias resistor (when the cathode resistor is un-bypassed).
If u= 6.5, and the un-bypassed cathode resistor is 100 Ohms, then rp increases by 650 Ohms.
Tradeoffs.
u x cathode bias resistor (when the cathode resistor is un-bypassed).
If u= 6.5, and the un-bypassed cathode resistor is 100 Ohms, then rp increases by 650 Ohms.
Tradeoffs.
If you "run" the 12B4's numbers, you will find (IMO) a manageable 15 Kohm Mills MRA-12 load resistor, along with a 20 mA. plate current, is suitable in combination with an unbypassed 500 Ω cathode bias resistor.
Not such a big fan of bypassed cathodes. Or cathodes that need bypassing. Go nuts, rig a small fixed bias scheme for them.
There are other options, 6AH4, 6CK4 come to mind. With a fixed bias scheme, you could also run 6BL7...which are reputed to be unmatched, but IME were really not so bad...LOL
Cheers,
Douglas
There are other options, 6AH4, 6CK4 come to mind. With a fixed bias scheme, you could also run 6BL7...which are reputed to be unmatched, but IME were really not so bad...LOL
Cheers,
Douglas
I believe I will try the 12b4a as I have several. The numbers that Eli mentions would need a B+ of around 400 volts, unless I am mistaken. A bit excessive as I would only need a little in excess of 300 volts for the output tubes. Perhaps for the 12b4a 150 volts plate, -20 volts bias at 20 ma, 1k resistor and 6.5k plate resistor?
Eli,
You are correct.
The OP wanted to use a transformer at the input to do the phase splitting.
Using precision tolerance un-bypassed self bias resistors and precision plate load resistors, will help to make up for any gain differences of the two 12B4.
I mistakenly thought he wanted to use an Interstate transformer.
That can have problems, because many interstage transformer's frequency response rolls off at both low frequencies and high frequencies.
Some interstage transformers do not work as well when the plate resistance, rp, is not many times lower than the "rated" interstage transformers impedance.
The frequency response is affected by the primary's inductance, and distributed capacitance.
You are correct.
The OP wanted to use a transformer at the input to do the phase splitting.
Using precision tolerance un-bypassed self bias resistors and precision plate load resistors, will help to make up for any gain differences of the two 12B4.
I mistakenly thought he wanted to use an Interstate transformer.
That can have problems, because many interstage transformer's frequency response rolls off at both low frequencies and high frequencies.
Some interstage transformers do not work as well when the plate resistance, rp, is not many times lower than the "rated" interstage transformers impedance.
The frequency response is affected by the primary's inductance, and distributed capacitance.
6S19P-V | Tubes Information
This Russian indirectly heated triode has Rp around 400 Ohms and mu near 3-4.
This Russian indirectly heated triode has Rp around 400 Ohms and mu near 3-4.
VladimirK,
Nice tube!
I do low power amplifiers, so I would use that tube as an Output tube, not a line amp tube.
Nice tube!
I do low power amplifiers, so I would use that tube as an Output tube, not a line amp tube.
The 7233 is similar... https://frank.pocnet.net/sheets/142/7/7233.pdf
It would be linear with a CCS, maybe not great with a resistive load.
It would be linear with a CCS, maybe not great with a resistive load.
Use a 10M45S CCS as the plate load and a 300 V. B+ rail is more than sufficient. AAMOF, 150 V. is quite sufficient. "Replicate" the provided schematic.
Attachments
With a 1:4 step-up you can use a DHT like 10Y, 26, 46, 47, 2P29L, 12A, 4P1L etc. Or a 01A with a cathode/source follower. See Bartola Valves for exactly this using a 47 tube. Best sound if you get it all right.
In indirectly heated tubes I'm fond of the EL33 myself, used with a plate choke.
In indirectly heated tubes I'm fond of the EL33 myself, used with a plate choke.