Wonderland/JM100 build

[martin manning]

Which 68k did you increase to 100k? Is it the one in the 1M/68k divider?

[norburybrook]

yes.

I've ben talking with jelle on the amp builders facebook page and he says the pictures of the JM amp don't show 1M-68K , he recons to try 180k into 68K.

need to sort this hum out first.

bugger!!!!



Marcus

[pompeiisneaks]

yes.

I've ben talking with jelle on the amp builders facebook page and he says the pictures of the JM amp don't show 1M-68K , he recons to try 180k into 68K.

need to sort this hum out first.

bugger!!!!



Marcus

Yeah we need to convince jelle to get back on here more often. I see him all the time on fb as well

Sent from my LG-V521 using Tapatalk

[dhudson]

ouch,. now there is an argument for a fuse on that secondary HT? better check them diodes!

[norburybrook]

ouch,. now there is an argument for a fuse on that secondary HT? better check them diodes!

Dave,Martin

I've done every combination of the valves and it's still the same hum.So can I assume that the valves are fine?


the amp sounds great, voltages are still all good, I presume then that the diodes are fine.


Ok, here's a weird one. the heater string is now showing 6vAC on one side and 0 on the other. I'm sure it was 3 and 3 when I checked

could that be a pointer?

Marcus

[martin manning]

What are filament voltages with all valves (including preamp) removed?

[dhudson]

that would cause hum for sure, one side of the heaters is grounded or shorted,.

[norburybrook]

same, 6 on one side 0 on the other

M

[martin manning]

Disconnect the PT filament leads and measure at the source. Also measure resistance to ground from each side of the filament wiring and verify 100R.

[norburybrook]

there 6 vAC between the secondary's.

each side of the filament is 100R

M

[martin manning]

That's good news. Reconnect the PT leads and put valves back in one at a time and check voltage from each side to ground.

[norburybrook]

1st 6l6 I put in measured 6 and 0

M

[martin manning]

Try a 6L6 from another amp. Is it back to 3V each side with no valves in?

[pompeiisneaks]

ouch,. now there is an argument for a fuse on that secondary HT? better check them diodes!

Dave,Martin

I've done every combination of the valves and it's still the same hum.So can I assume that the valves are fine?


the amp sounds great, voltages are still all good, I presume then that the diodes are fine.


Ok, here's a weird one. the heater string is now showing 6vAC on one side and 0 on the other. I'm sure it was 3 and 3 when I checked

could that be a pointer?

Marcus

It depends on how you measure the voltage. If you measure from ground each leg is 3 volts. If you measure leg to leg you're going to get 6.3 if you accidentally measure leg to the same leg you're getting 0v

Sent from my LG-V521 using Tapatalk

[norburybrook]

Try a 6L6 from another amp. Is it back to 3V each side with no valves in?

No it's 6 and 0 with no valves in.

M