I don't like that project. The 300B must be driven from linear stuff similar to it. In this way the first stage with 6922 in srpp and the second stage with 6H30 also in srpp is a good choiche. in case you can use a single E88C (not E88CC) in SRPP, it is a very interesting solution because is involed only one amplification stage to drive the 300B why not E88C
Walter
Walter
Maybe is an error on drawining the circuit. The intention is to use the pentode as triode. In addition this circuit is using a 5u4 with 310+310 vac (and a mix of fixed an cathode bias) the Vdc is low to reach a right power. In every case I can't undersand the use of a pentode as triode when there are other stuff bettere than this solution
Last, the OT must be a the best this to justify the money to buy a pair of 300B
Walter
Last, the OT must be a the best this to justify the money to buy a pair of 300B
Walter
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Look this:
6H30PI Sovtek :: Sovtek :: Tubes :: Banzai Music GmbH same tube, with 10% more you can ask for matching.
or
www.thetubestore.com - Russian 6N6p / 6H6pi Audio Tubes
Walter
6H30PI Sovtek :: Sovtek :: Tubes :: Banzai Music GmbH same tube, with 10% more you can ask for matching.
or
www.thetubestore.com - Russian 6N6p / 6H6pi Audio Tubes
Walter
Hi xcicc,
Wow, this is my first post to this forum.
Ok, whilst your circuit diagram is incorrect - g1 and g2 are transposed on the pentode half of the ECL82, it's nice to see -ve feedback being used in a SE triode amp.
As a first-poster, i must be careful what i say but my favourite way of driving a 300B (or any output triode) is a 5687 wired in SRPP "series boot-strap", as this gives you the voltage gain (µ of the triode) and the drive current from the cathode of the upper of the two triodes.
Xx.
Wow, this is my first post to this forum.
Ok, whilst your circuit diagram is incorrect - g1 and g2 are transposed on the pentode half of the ECL82, it's nice to see -ve feedback being used in a SE triode amp.
As a first-poster, i must be careful what i say but my favourite way of driving a 300B (or any output triode) is a 5687 wired in SRPP "series boot-strap", as this gives you the voltage gain (µ of the triode) and the drive current from the cathode of the upper of the two triodes.
Xx.
I don't see anything wrong in using an ECL82 as a driver for the 300B. I might, though, opt for using the pentode half to drive the output tube directly. But that poses additional considerations to the design. As long as it's kept in class A1 operation, there should be not much trouble with the schematic posted, given that the driver tubes are wired correctly and not as they're shown in the schematic. It won't probably extract every last inch of what you can get out of a 300B, but I'd expect it to work just fine.
Some considerations, though. The +B voltage is quite low as already mentioned, especially with a tube rectifier. Secondly, I'm not quite sure that a 5U4 would enjoy that much input capacitance. 100µF might just be eating away it's useful life faster than necessary.
Third thing to consider is the feedback loop. This should be applied only when you've measured the thing open loop, and can assess it's response both in the amplitude and phase domain, lest you wish oscillations to occur. Many conventional transformers drop their response quite gracefully, but some - especially toroidals, I've found - have some quite nasty high frequency resonances, which can spell big trouble. If you want to do things right, you'll need measuring capabilities at least up to 1 MHz.
Now, if I was designing a 300B amp, I'd probably go with a single pentode driver stage with high quiescent current and a low plate load resistor. That'd give enough gain from a single stage, and a low enough driving impedance for the output tube. Or a high gain triode and a buffer. Either option would give the option of tailoring the distortion behaviours of the driver and output stage to match and partially cancel out before global feedback was applied.
Some considerations, though. The +B voltage is quite low as already mentioned, especially with a tube rectifier. Secondly, I'm not quite sure that a 5U4 would enjoy that much input capacitance. 100µF might just be eating away it's useful life faster than necessary.
Third thing to consider is the feedback loop. This should be applied only when you've measured the thing open loop, and can assess it's response both in the amplitude and phase domain, lest you wish oscillations to occur. Many conventional transformers drop their response quite gracefully, but some - especially toroidals, I've found - have some quite nasty high frequency resonances, which can spell big trouble. If you want to do things right, you'll need measuring capabilities at least up to 1 MHz.
Now, if I was designing a 300B amp, I'd probably go with a single pentode driver stage with high quiescent current and a low plate load resistor. That'd give enough gain from a single stage, and a low enough driving impedance for the output tube. Or a high gain triode and a buffer. Either option would give the option of tailoring the distortion behaviours of the driver and output stage to match and partially cancel out before global feedback was applied.
The essential effect of the 300B fixed negative bias circuit is 250VAC driving a half wave rectifier, driving a 10k/10k 2:1 divider. That is (1.414 x 250V) / 2 = -176Volts.
The schematic should either use fixed Bias (but adjustable fixed), or Self Bias.
The 820 Ohm and bypass cap is self bias.
The fixed bias (-176) could be used instead, but only if it is revised, and the self bias circuit is removed.
The schematic should either use fixed Bias (but adjustable fixed), or Self Bias.
The 820 Ohm and bypass cap is self bias.
The fixed bias (-176) could be used instead, but only if it is revised, and the self bias circuit is removed.
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