27-01-2020, 05:54 PM
(This post was last modified: 27-01-2020, 06:01 PM by Diabolical Artificer.)
What are you using as the input? Too much IP can cause distortion of the OP but wouldn't really explain the low OP level. You say you've checked DC voltages but check again the grids in relation to ground but also check the grids in relation to the cathodes. the ECC83 should be around 1-2v and the EL84 around 7v.
Have you a scope? A comparison of the input waveform to the OP is beneficial, as is having a look at the signal on each grid and anode. Make sure you don't exceed your scopes IP Vmax. You can use a 0.1u 630v cap or any other cap of around that value on your scope probe to block high voltage DC to be on the safe side.
Finally you can check the OPT with a DC resistance check. Unplug the EL84 then check DC resistance from pin 6 to ground, then with the speaker disconnected check the secondary. Primary DC R should be around 100r ish +, the secondary a few ohms. There might be a HV cap on the primary side and possibly a resistor, make sure these aren't effecting your reading. You can also have a listen and a sniff around the OPT, any buzzing or,nasty smell is indicative. You can also check the OPT with a screwdriver, put the plaggy end against your ear, metal end on the OPT laminations.
Andy.
PS, including a schematic is alus a good idea when posting a query.
Have you a scope? A comparison of the input waveform to the OP is beneficial, as is having a look at the signal on each grid and anode. Make sure you don't exceed your scopes IP Vmax. You can use a 0.1u 630v cap or any other cap of around that value on your scope probe to block high voltage DC to be on the safe side.
Finally you can check the OPT with a DC resistance check. Unplug the EL84 then check DC resistance from pin 6 to ground, then with the speaker disconnected check the secondary. Primary DC R should be around 100r ish +, the secondary a few ohms. There might be a HV cap on the primary side and possibly a resistor, make sure these aren't effecting your reading. You can also have a listen and a sniff around the OPT, any buzzing or,nasty smell is indicative. You can also check the OPT with a screwdriver, put the plaggy end against your ear, metal end on the OPT laminations.
Andy.
PS, including a schematic is alus a good idea when posting a query.
