19-04-2011, 05:58 PM
Thanks, Steve; I'm starting to feel like cracking myself one with the EHT.
I've re-done those readings with both my AVO and DMM with the following results:
Pin 2 to earth = 6.5v (6.49v)
Pin 3 to earth = 12.5v (12.42v)
Pin 3 to 2 = 2.2v (1.72v)
Disconnecting R23 didn't make much odds, it may have reduced the overall volume a bit but that was all.
I'd already replaced C49 but took it out and tested it and that was OK.
The main problem today has been a loud constant hum which is there no matter what the volume is set to or whether it's on a wave-length or Gram. There was also some distortion but it didn't sound mechanical. However, I've got a spare 3 ohm speaker so tried it with that and it was fine. There's still a background hum but nothing like as bad and no circuit, old or new, is totally silent. The voltages quoted above were the same. Sadly this speaker is a round ten inch one so can't be used as a simple replacement. I'm really not sure what's up with the original as the cone doesn't feel scrunchy and it sounded fine this morning with a transistor playing through it out of the case.
I've got a Grundig reel-to-reel tape recorder in the loft so I'll have a look what valves that's got in it.
If it doesn't behave itself I'll have to start looking up trans-Pennine train services!
Thanks for your help.
All the best
Joe
I've re-done those readings with both my AVO and DMM with the following results:
Pin 2 to earth = 6.5v (6.49v)
Pin 3 to earth = 12.5v (12.42v)
Pin 3 to 2 = 2.2v (1.72v)
Disconnecting R23 didn't make much odds, it may have reduced the overall volume a bit but that was all.
I'd already replaced C49 but took it out and tested it and that was OK.
The main problem today has been a loud constant hum which is there no matter what the volume is set to or whether it's on a wave-length or Gram. There was also some distortion but it didn't sound mechanical. However, I've got a spare 3 ohm speaker so tried it with that and it was fine. There's still a background hum but nothing like as bad and no circuit, old or new, is totally silent. The voltages quoted above were the same. Sadly this speaker is a round ten inch one so can't be used as a simple replacement. I'm really not sure what's up with the original as the cone doesn't feel scrunchy and it sounded fine this morning with a transistor playing through it out of the case.
I've got a Grundig reel-to-reel tape recorder in the loft so I'll have a look what valves that's got in it.
If it doesn't behave itself I'll have to start looking up trans-Pennine train services!
Thanks for your help.
All the best
Joe
