Still got PCB left.simon wrote:
If you go to a directly heated driver, whether a 4P1L pentode say or another triode, then you need to get the filament supply right as it will hum like a good 'un. Andrew L here has developed some boards and might still have some, or try Rod Coleman on DIY Audio, whose boards are also very good. Or lots of chokes
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#16
Analogue, the lost world that lies between 0 and 1.
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#20
Suck it and see. It's the only way you'll find out what you prefer.Tomas wrote:Hi Mark, You're saying that a cap coupled C3g in pentode to 45 would be preferable to The IT that I have available?
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#22
If done correctly then I would have that opinion based on my ears and my recent projects . For instance my current amp was C3g pentode into KR300B , now uses a DHP ( 4P1L ) into 300B , and I'm not intending to change ( btw. I did run ECC40/45(choke-loaded)/300B for a spell in the past ) .Tomas wrote:Hi Mark, You're saying that a cap coupled C3g in pentode to 45 would be preferable to The IT that I have available?
It's not going to be clear-cut, as there are system decisions to be made of course, and listening preferences.
Comparing C3g triode with by-passed cathode, and C3g pentode with un-bypassed cathode and about 8k anode load, you'll get slightly more gain ( 50? ) with the pentode, which may be irrelevant .
In the mids and treble , it's a bit dependant on the IT's which I would say is best - I'd want to see at least 50% nickel core in the IT's to match or beat a good cap & resistor .
In the bass I'm sold on the pentode option if used with a VR tube for the G2 . The pentode is nearly linear down to DC then, because it has no cathode by-pass cap and the cap/resistor coupling can be down around 1Hz cut-off with something like 0.47u/220k into the 45 . The triode/IT combo, on the other hand, has a cathode cap that might be 2Hz , and the IT inductance ( limited in SE transformers ) might give only 5 to 10Hz -3dB point . This will take away a bit of timing and low-bass tone .
If you've got the parts, and just want to build a neat chassis without a re-build, then don't let me stop you. The C3g/IT/45 will be a very nice amp. If you have the time, though , a breadboard to compare that against C3g pentode would be good.
"Once you find out ... the Circumstances ; then you can go out"
#23
Thanks very much for the info and insight Mark. I suppose I have a couple of chokes on my hands to use for a future project. In a way the IT's were restricting my choices as I was pretty committed to trying to use them. This will open things up a lot and allow me to go in a new direction for a 2 stage. Thanks again.