The swing you require depends entirely on where you run the GM70.
To increase swing with a pentode driver increase the plate load resistance and supply voltage. You will usually have to adjust the plate voltage upwards as well to move the operating point further away from the plate curve kinks. It's pretty easy to do once you obtain a graph of the curves. All you need is a ruler.
To increase swing with a pentode driver increase the plate load resistance and supply voltage. You will usually have to adjust the plate voltage upwards as well to move the operating point further away from the plate curve kinks. It's pretty easy to do once you obtain a graph of the curves. All you need is a ruler.
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Pentode - Triode
General question, why build an amp with a pentode front end tube, when a REAL triode tube is available ?
Also, Thorsten's implementation of the pentode is soo soo common, and so sub-optimal, a drop-down resistor from the main B+, and a cap to ground !!! Ugh.
A pentode really should have a TOTALLY SEPARATE grid supply, if you want to do a pentode "right" as possible !!
Easier and better to use a triode, without that extra grid in the way, say I !!
Jeff Medwin
General question, why build an amp with a pentode front end tube, when a REAL triode tube is available ?
Also, Thorsten's implementation of the pentode is soo soo common, and so sub-optimal, a drop-down resistor from the main B+, and a cap to ground !!! Ugh.
A pentode really should have a TOTALLY SEPARATE grid supply, if you want to do a pentode "right" as possible !!
Easier and better to use a triode, without that extra grid in the way, say I !!
Jeff Medwin
deafbykhorns, a properly implemented pentode driver can sound excellent. I have used a variant of the posted C3g driver schematic with gas tube regulated screen and can vouch for its ability.
The g-k voltage on the schematic you posted is a whopping 128V, so you would be aiming at being able to generate at LEAST 150V clean swing each way. You would therefore be looking at a Vp of around 250V for a C3m driver, which would limit you to around 16-17mA current (I am looking at the Vg2=150V curves here btw).
The advantage with using a pentode in this application is that you only need the one tube and can also dispense with the costly interstage iron.
Other candidates that come to mind are the D3a, C3g, EL84 or perhaps the Russian 6P15-EV. A 12AX7 simply won't work in this application.
The g-k voltage on the schematic you posted is a whopping 128V, so you would be aiming at being able to generate at LEAST 150V clean swing each way. You would therefore be looking at a Vp of around 250V for a C3m driver, which would limit you to around 16-17mA current (I am looking at the Vg2=150V curves here btw).
The advantage with using a pentode in this application is that you only need the one tube and can also dispense with the costly interstage iron.
Other candidates that come to mind are the D3a, C3g, EL84 or perhaps the Russian 6P15-EV. A 12AX7 simply won't work in this application.
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Not my words that follow, in discussion on 12-24-15 of Solid State vs FILAMENTARY rectifiers on efficient speakers ( the kind of speaker you use with tube amps !! )
RE: tube rectifiers: cannot detect differences with my Quads...only on the Khorns-nT - Cleantimestream - Tube DIY Asylum
I use the new JJ 5U4GB, very nice filamentary rectifier tube !!
2A3 DC Article - 1994
Goldenbeer:
Ever see this one !! Lovely article, take a look.
IspraNet Audio: Direct Coupled Single Ended Amplifier
My 2015 vote is half a vintage smooth plate Telefunken, etc. 12AX7, DCed into a modern JJ 2A3-40 and use of a JJ 5U4GB rectifier tube. L1/C1/L2/C2 filter to 2A3 Finals, with all Ls under 10 ohms DCR.
Goldenbeer:
Ever see this one !! Lovely article, take a look.
IspraNet Audio: Direct Coupled Single Ended Amplifier
My 2015 vote is half a vintage smooth plate Telefunken, etc. 12AX7, DCed into a modern JJ 2A3-40 and use of a JJ 5U4GB rectifier tube. L1/C1/L2/C2 filter to 2A3 Finals, with all Ls under 10 ohms DCR.
More common are people who don't know how a Loftin-White works.
Really?
In fact they haven't built any Loftin-White. They have only made a simplistic DC coupled amp.
Your right, it didn't seem to do anything for the circuit after running the sim.
However, my bandwidth is really bad after the pentode, almost a 5 db drop at 20hz.
I like my SIM of the 6BL7 better, it seems to drive the GM 70 into A2 slightly when needed.
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What's the reflected load back to the driver from the interstage transformer?
Yes, I simmed 124
The plot is after the pentode before the cap, that's were I read the drop in freq. response(which of course carried thru the IT and OPT).
IT is 5k, is that bad to use this with a 6bl7? I thought it would be better if the grid starts pulling some current on peaks. Plots look pretty good or am I missing something?
The plot is after the pentode before the cap, that's were I read the drop in freq. response(which of course carried thru the IT and OPT).
IT is 5k, is that bad to use this with a 6bl7? I thought it would be better if the grid starts pulling some current on peaks. Plots look pretty good or am I missing something?
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Then the bass rolloff is because of the time constant of the 0u47 coupling cap and the IT load. Nothing mysterious; f3 calculates out to 65Hz or so if it's a 5k load.
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