Ok, before you deem the PT defective (which could still be a valid diagnosis), I would disconnect the A and C point wires of the transformer from the rectifier board. Measure the voltage between the wires (keep the standby switch off !!) . Getting only 1-5V between those two wires really sticks out. Could be something in the low voltage circuit throwing everything else off.
The Mojotone replacement part is as close as you can get to NOS, afaik they obtained the remaining stock of parts from Ernie Ball after the Music Man amp division was dismantled - but most of the parts available from them by now are newly manufactured replicas if one can say so. If you have to replace the power transformer you need to convert to the new style where the hi/lo is switched on the secondary. You can still maintain the 12AX7 etc - you just have to rewire a bit. I've done it and am quite happy with the result.
Another excellent idea, will definitely test that tonight and report back. But first...
Are you saying to pull the plastic covered red and black wires at points A and C and measure between them, or pull the cloth covered transformer wires which feed them (two orange or one orange and one yellow/red)?
Also: when you say "keep the Standby switch off" - you mean keep it in its Off position, as opposed to its On position, which is where you set it to actually take it off Standby and play the amp...
Sorry, I guess that wasn't really clear. The reason I say keep the standby on 'off' (as in no B+ to the tubes) is to avoid damaging the tubes. With no low voltage supply, the bias voltage is gone and there's not telling what the power tubes might do.
Not sure what exact voltages you should see between those two wires without any load - but it should be beyond 110V AC on both lo and hi.
Be careful regarding WHICH transformer is in your amp!
The early Music Man amps switched from high power to low power by changing a tap on the PRIMARY of the power transformer, which caused ALL voltages to dip in the amp. People complained about this and MM changed the transformers so that the low/hi power switch controlled a tap selection on the secondary winding of the high voltage section ONLY.
My 1974 410-65 has the screwy early transformer (with 12AX7) and my 1977 410-65 has the newer/better transformer (and no 12AX7). I much prefer to play the 1977 model because of this.
The 65 & 130 series schematics show BOTH of these generations, just pay close attention and you will see this. FYI... the transformer part numbers are also different so you can tell from that as well. I do not know if this is what you are fighting but it could well be!
The only numbers I can find on my '74 210-Sixty-Five PT is the EIA code, 606-4-09 which translates to Woodward - Schumacher manufactured the 9th week of 1974. The schematic in the documents that came with amp list it only as a 100-65 XFMR. Have to check the codes on the '76 amp, but everything else in it dates to early '76.
Seems odd that two amps configured the same way (and recapped by me) should have such different sonic characteristics - one breaks up considerably at Volume 3, the other goes to nearly twice that clean. Be curious to see what voltages you are getting in your 410 Sixty-Five.
Check the low voltage
Ok, before you deem the PT defective (which could still be a valid diagnosis), I would disconnect the A and C point wires of the transformer from the rectifier board. Measure the voltage between the wires (keep the standby switch off !!) . Getting only 1-5V between those two wires really sticks out. Could be something in the low voltage circuit throwing everything else off.
The Mojotone replacement part is as close as you can get to NOS, afaik they obtained the remaining stock of parts from Ernie Ball after the Music Man amp division was dismantled - but most of the parts available from them by now are newly manufactured replicas if one can say so. If you have to replace the power transformer you need to convert to the new style where the hi/lo is switched on the secondary. You can still maintain the 12AX7 etc - you just have to rewire a bit. I've done it and am quite happy with the result.
Cheers,
Lars Verholt
Another excellent idea, will
Another excellent idea, will definitely test that tonight and report back. But first...
Are you saying to pull the plastic covered red and black wires at points A and C and measure between them, or pull the cloth covered transformer wires which feed them (two orange or one orange and one yellow/red)?
Also: when you say "keep the Standby switch off" - you mean keep it in its Off position, as opposed to its On position, which is where you set it to actually take it off Standby and play the amp...
What kind of voltages should I see?
When I say 'off' I mean 'amp is on standby'
Sorry, I guess that wasn't really clear. The reason I say keep the standby on 'off' (as in no B+ to the tubes) is to avoid damaging the tubes. With no low voltage supply, the bias voltage is gone and there's not telling what the power tubes might do.
Not sure what exact voltages you should see between those two wires without any load - but it should be beyond 110V AC on both lo and hi.
Cheers,
Lars Verholt
Thanks for the clarification.
Thanks for the clarification.
So...which specific wires am I measuring between, the two orange or one orange and one yellow/red (all cloth covered from the PT)?
Unsoldered the two orange
Unsoldered the two orange cloth covered wires coming from the PT and measured.
'74 210 Sixty Five
Low - 23.06 V AC
High - 34.64 V AC
'76 112 Sixty Five
Low - 31 V AC
High - 35 V AC
Assuming I did it correctly, the low winding still seems very low.
Be careful regarding WHICH transformer is in your amp!
The early Music Man amps switched from high power to low power by changing a tap on the PRIMARY of the power transformer, which caused ALL voltages to dip in the amp. People complained about this and MM changed the transformers so that the low/hi power switch controlled a tap selection on the secondary winding of the high voltage section ONLY.
My 1974 410-65 has the screwy early transformer (with 12AX7) and my 1977 410-65 has the newer/better transformer (and no 12AX7). I much prefer to play the 1977 model because of this.
The 65 & 130 series schematics show BOTH of these generations, just pay close attention and you will see this. FYI... the transformer part numbers are also different so you can tell from that as well. I do not know if this is what you are fighting but it could well be!
Steve
The only numbers I can find
The only numbers I can find on my '74 210-Sixty-Five PT is the EIA code, 606-4-09 which translates to Woodward - Schumacher manufactured the 9th week of 1974. The schematic in the documents that came with amp list it only as a 100-65 XFMR. Have to check the codes on the '76 amp, but everything else in it dates to early '76.
Seems odd that two amps configured the same way (and recapped by me) should have such different sonic characteristics - one breaks up considerably at Volume 3, the other goes to nearly twice that clean. Be curious to see what voltages you are getting in your 410 Sixty-Five.
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