28-12-2016, 04:40 PM
(This post was last modified: 28-12-2016, 04:41 PM by Murphyv310.)
Hi.
This set has sent me on a merry dance. It's rest of two years seems have greatly improved the tracking, the tuning is now nearly spot on but the other AGC problem has left me scratching my head
Initially I had bad distortion on strong stations and only about -2v AGC. Since I have had another go I have replaced the EBF2 double diode vari mu pentode with an EF9 and strapped in two germanium diodes and have -3.5v AGC now, I'm sure it's too low though. The IF's are 465Khz on this set and I did a full realignment to no avail. I have been around the circuit with a fine toothcomb with no success, the set is sensitive and pulls in weak stations with ease, audio quality is spot on on the weaker stations.
One thing does come to mind and that is the odd EFM1 combined tuning indicator and AF amp, the tuning indicator is duff with nothing seen, voltages seem fine but I am now thinking of using an EF92 as the AF amp (it needs to be Vari MU due to the circuit design) and seeing if doing that may help, I'm not hopeful though.
I have a copy of the circuit from the Radio Museum but I don't think I should post it here due to copyright.
Perhaps if someone has the sheet then I'd like to post it here.
Any ideas fellas?
This set has sent me on a merry dance. It's rest of two years seems have greatly improved the tracking, the tuning is now nearly spot on but the other AGC problem has left me scratching my head
Initially I had bad distortion on strong stations and only about -2v AGC. Since I have had another go I have replaced the EBF2 double diode vari mu pentode with an EF9 and strapped in two germanium diodes and have -3.5v AGC now, I'm sure it's too low though. The IF's are 465Khz on this set and I did a full realignment to no avail. I have been around the circuit with a fine toothcomb with no success, the set is sensitive and pulls in weak stations with ease, audio quality is spot on on the weaker stations.
One thing does come to mind and that is the odd EFM1 combined tuning indicator and AF amp, the tuning indicator is duff with nothing seen, voltages seem fine but I am now thinking of using an EF92 as the AF amp (it needs to be Vari MU due to the circuit design) and seeing if doing that may help, I'm not hopeful though.
I have a copy of the circuit from the Radio Museum but I don't think I should post it here due to copyright.
Perhaps if someone has the sheet then I'd like to post it here.
Any ideas fellas?
