I see two issues: FU32 G2 has a datasheet limit of 250V, but on the schematic (post #20) the value is 294V; maximum G2 value for 6J1P is between 155V and 160V, on this schematic we have 176V. Dropping a little bit the FU32 G2 voltage by adding R1/C3 is a good idea anyway and I will try it. It would be useful to have the 832A / FU32 anode curves plotted with G2 = 200V, to compare them with the curves at G2 = 250V I already have, but I was not able to find them on my datasheets.
As long as we do not exceed the absolute limit data given by the catalog sheet, I do not think we should be in trouble. We always have to keep in mind that the maximum power dissipated, so the voltage to current ratio can be anywhere in the limit which do not exceed the dissipated power and the limit data recommended by the manufacturer. Do not worry, the catalog sheets are somewhat informative and we can not even take them as a law, many know what I mean. The only component on the schematic whose value should the choice is practically the value of the R2 resistance so that it does not exceed the anode current by passing the final tube more than 45mA .... 50mA, the rest will guarantee that everything will work perfectly! I wish you success!
Ra must be 6500 ohms, so the results will be very good!
Ra must be 6500 ohms, so the results will be very good!
Thanks for all the info! I'm looking forward to the build. 🙂
And I went and ordered a few GU-32's x the former soviet block after reading some less than complimentary observations about the chinese tubes.
And then I went and bought a few more with the idea of building a RLD amp with them - looks like that'd be a bit of fun. 🙂
It's actually quite a lovely wee kit. Certainly for the price, I'm quite happy!
I'll post some photos once I get the phone to upload photos to diyaudio properly...
And I went and ordered a few GU-32's x the former soviet block after reading some less than complimentary observations about the chinese tubes.
And then I went and bought a few more with the idea of building a RLD amp with them - looks like that'd be a bit of fun. 🙂
It's actually quite a lovely wee kit. Certainly for the price, I'm quite happy!
I'll post some photos once I get the phone to upload photos to diyaudio properly...
I had a stereo 807 amp from a well known builder who sells on eBay on my bench a few weeks ago built with a pair of Chinese 5K transformers that look identical to the ones on that FU-32 amp. While the amp made about 8W at 1kHz/10% THD, it made less than 1/4 of a watt at 35Hz/10% THD, and I would have to attribute that to these transformers. You can get them on AliExpress for about $12. For a headphone amp or a preamp, they might be OK.
Could anybody summarize all the mods for this circuit? Thanks.
I just finished the chinese diy kit. It sounds great.
There is also a review on the valve museum page. Just google, direct link doesn't work.
I just finished the chinese diy kit. It sounds great.
There is also a review on the valve museum page. Just google, direct link doesn't work.
I built the amplifier, a 65$ kit, 15$ for the tubes extra and 60$ delivery to Europe. Works fine, warm sound, gets rather hot but ok, livingroom level, no noise or hum, all ok.
6A3sUMMER added this mods. Thx very much!
Connect a 10uF cap from FU32 pin 3 to ground. that bypasses the 2k resistor to ground
B+ is less than 300V, but is much higher before the FU3 warms up. Use a 10uF thta has a 500V rating.
FU32 connect a 1k resistor from pin2, to the junction of O.1uf and 300k.
FU32 connect a 1k resistor from pin,6 to the junction of O.1uf and 300k.
These 1 k resistors are called grid stopper resistors.
Connect the junction of the. 0.1uf and 300k Ohm resistor to one side of the added 1k resistor. connect the other side of the added 1k resistor directly to the tube socket tab pin2.
Connect the junction of the. 0.1uf and 300k Ohm resistor to one side of the added 1k resistor. connect the other side of the added 1k resistor directly to the tube socket tab pin6.
6A3sUMMER added this mods. Thx very much!
Connect a 10uF cap from FU32 pin 3 to ground. that bypasses the 2k resistor to ground
B+ is less than 300V, but is much higher before the FU3 warms up. Use a 10uF thta has a 500V rating.
FU32 connect a 1k resistor from pin2, to the junction of O.1uf and 300k.
FU32 connect a 1k resistor from pin,6 to the junction of O.1uf and 300k.
These 1 k resistors are called grid stopper resistors.
Connect the junction of the. 0.1uf and 300k Ohm resistor to one side of the added 1k resistor. connect the other side of the added 1k resistor directly to the tube socket tab pin2.
Connect the junction of the. 0.1uf and 300k Ohm resistor to one side of the added 1k resistor. connect the other side of the added 1k resistor directly to the tube socket tab pin6.
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