| Triode Amplifier |
| I made a tetrode amplifier (GK amplifier)
myself, but I had no experience making a triode amplifier (GG
amplifier), so I received a 3CPX800 triple parallel from someone. I was
told it was broken, so I turned it on hesitantly. Normally, vacuum tubes
have a warm-up period of about 3 minutes, but it didn't reach that point
and the protector was activated, so it was NG. I thought the tube was NG,
so I removed all the tubes and turned the power on, but there was no
problem. I tried it with just one tube, but it was NG. It seemed like the
plate current was abnormal, so maybe the tube was bad? I looked into it,
and found that the zener of the cathode bias was passing through. I had
heard about it in the past, but I was asked if anyone had a zener with a
large wattage because I would need to change the zener to change the bias
current, but I finally understood when I touched it myself. So I changed
it to a circuit that can be continuously adjusted with a semi-fixed VR
without changing the zener diode, so I will introduce it here. When you
swing the bias current back and forth, you can see a 5-8dB change
(improvement) in the IMD characteristics. If you try it, do so at your own
risk. No complaints. The appearance is also pretty clean, and it's a great
amplifier. I thought I'd get a spare vacuum tube, but while "3CX800" is common, this unit is "3CPX800", and when it has a P, the maximum plate applied voltage is higher than 2500V, so I haven't been able to get a 3500V vacuum tube yet. Currently, I mainly use triode amplifiers, and tetrode amplifiers don't match the usage environment due to their weight and noise. The case was a big failure. |
Schematic File |
３本3CPX800 3 pieces |
exterior |
High voltage transformer |
Modification of the bias adjustment circuit of
this unit |
|
|
Four previous failures ①The return (GND) of the vacuum tube filament current is GND via the board mounting screw, so no radio waves are emitted if the pattern comes off. ＜countermeasure＞The lead wire is fixed to GND. ②Transmission is OK, but when receiving, the receiving ANT does not connect properly. ＜countermeasure>The contacts of the transmitting and receiving relays were faulty, so they were replaced with new Omron 16A relays. The same fault occurred twice. ③The earth leakage breaker tripped when the primary side (200V) was applied. ＜countermeasure＞Lightning caused a short circuit in the bypass capacitor between the primary side and GND. The three vacuum tubes are still going strong. |
|
| Tetrode Amplifier |
| It is based on an amplifier that I received from a friend as a broken item, and when I tried to repair it, many of the parts such as the high voltage transformer and relays were no good, but the vacuum tubes seemed to be OK, so I asked my friend for advice and gathered the missing parts to make it. It's not something I can really recommend, but the case was also made at an acquaintance's ironworks, but it was a complete failure. The ultimate goal is to have a preset tune function, but we are not there yet. Once it is completed to the final specifications, I will improve the appearance of the case and upload it again. I don't want to write the names of the vacuum tubes because it will lead to a prediction of the power, but when I use it with this, it only produces around 1kW of power. If I make it more powerful, it becomes a terrible signal. Some people might think that I am producing high power by writing excuses like this? ...Actually... |
4CX2500 imitation (GU84B) x 2 |
RF Block |
 |
Blow with a blower and suck with two book fans |