26-06-2012, 10:22 PM
Did a few more hours on the Regenerodyne project late this afternoon and this evening, made some progress, first I replaced the RF Amp (6AC7) with a 6SH7 as on the high frequencies the 6AC7 was starting to go into regeneration which I don't really want in the RF stage, the 6SH7 has an internal twin cathode connection lead out thus reducing the internal cathode lead inductance, the RF Amp now performs better with this valve fitted.
I decided to change the harmonic generator/amplifier from one half of the 6SC7 (triode) to the now spare pentode (6AC7) one of the reasons was that the other half of the 6SC7 is used as the first AF amp but unfortunately the valve has a common cathode so poss harmonics/RF getting into the audio line and maybe back through the HT or heater line.
I plumbed in the 6AC7 as a pentode connecting the control grid via a 100pf to the donor 1 Mhz osc in the B40D, I rewound the two anode tank coils (one for the low bands and one for the high bands) optimised the bias and screen voltage and fired it up, the results were a lot better than I expected, so much so that on tuning the harmonic selector tank to the 21st harmonic and peaking the RF tunining control for 18 Mhz I was rewarded by listening to a amature transmission from Venuzwalia (YV4EH) to a bloke in Bulgaria on 17 meters so really pleased with that, also now the mixing products from the harmonics either side of the tuned harmonic are somewhat reduced to what they were before.
Hear is are some rough unscientific test results:
Regenerodyne tuned to a medium strength European amature transmission around 18.1 Mhz using the 21st harmonic of the 1 Mhz donor osc. and manually tuned the sig gen which was set to full output on its attenuator (25 mv) and set to CW, its center insulated coax lead was wrapped round the aerial lead to give a bit of loose coupling, outer of the coax was left floating.
Tuned sig gen to received signal......blottoed as you would expect.
Lower harmonic products:
17.1 Mhz, quite noticable when tuned through the amature transmissionon on 18.1 Mhz but still able to resolve transmission ok.
16.1 Mhz, noticable but generally weak.
15.1, 14.1, 13.1 Mhz etc, nothing noticable.
Higher harmonic products:
19.1 Mhz, as 17.1 Mhz but weaker.
20.1 Mhz, as 16.1 Mhz but weaker still.
22.1, 23.1, 24.1 Mhz etc, nothing noticable.
During the above test the sig gen output was kept constant.
Unscientific I know but it gave me a good idea of what's what so far as listening tests go, also remember that nothing in the receiver is screened as yet (just the metal valves) overall quite encouraging, however the acid test will be from 18 Mhz up to 30 Mhz, this is unchartered territory as I have no RF or harmonic tank coils for those frequencies yet, I will attempt to wind some next time.
I did not have time to perform the above test down at 7 Mhz but I would think the results would be even better as the inductance Q's rise.
Since I started this project I have ascertained that it performs very well (in my opinion) from MW through to 18 Mhz, the audio quality on the SW broadcast transmissions is very good when the band conditions are good.
More to come I dare say.
Lawrence.
I decided to change the harmonic generator/amplifier from one half of the 6SC7 (triode) to the now spare pentode (6AC7) one of the reasons was that the other half of the 6SC7 is used as the first AF amp but unfortunately the valve has a common cathode so poss harmonics/RF getting into the audio line and maybe back through the HT or heater line.
I plumbed in the 6AC7 as a pentode connecting the control grid via a 100pf to the donor 1 Mhz osc in the B40D, I rewound the two anode tank coils (one for the low bands and one for the high bands) optimised the bias and screen voltage and fired it up, the results were a lot better than I expected, so much so that on tuning the harmonic selector tank to the 21st harmonic and peaking the RF tunining control for 18 Mhz I was rewarded by listening to a amature transmission from Venuzwalia (YV4EH) to a bloke in Bulgaria on 17 meters so really pleased with that, also now the mixing products from the harmonics either side of the tuned harmonic are somewhat reduced to what they were before.
Hear is are some rough unscientific test results:
Regenerodyne tuned to a medium strength European amature transmission around 18.1 Mhz using the 21st harmonic of the 1 Mhz donor osc. and manually tuned the sig gen which was set to full output on its attenuator (25 mv) and set to CW, its center insulated coax lead was wrapped round the aerial lead to give a bit of loose coupling, outer of the coax was left floating.
Tuned sig gen to received signal......blottoed as you would expect.
Lower harmonic products:
17.1 Mhz, quite noticable when tuned through the amature transmissionon on 18.1 Mhz but still able to resolve transmission ok.
16.1 Mhz, noticable but generally weak.
15.1, 14.1, 13.1 Mhz etc, nothing noticable.
Higher harmonic products:
19.1 Mhz, as 17.1 Mhz but weaker.
20.1 Mhz, as 16.1 Mhz but weaker still.
22.1, 23.1, 24.1 Mhz etc, nothing noticable.
During the above test the sig gen output was kept constant.
Unscientific I know but it gave me a good idea of what's what so far as listening tests go, also remember that nothing in the receiver is screened as yet (just the metal valves) overall quite encouraging, however the acid test will be from 18 Mhz up to 30 Mhz, this is unchartered territory as I have no RF or harmonic tank coils for those frequencies yet, I will attempt to wind some next time.
I did not have time to perform the above test down at 7 Mhz but I would think the results would be even better as the inductance Q's rise.
Since I started this project I have ascertained that it performs very well (in my opinion) from MW through to 18 Mhz, the audio quality on the SW broadcast transmissions is very good when the band conditions are good.
More to come I dare say.
Lawrence.
