Metro JTM 45 build instructions and pics

[?Mark]

I've comlpeted the build and double checked everything.
I'm am at the putting in tubes and taking measurements.
1st no tubes, voltages good.

Then rectifier, voltages good.

Then pre amps
V1, all good
V2, all good
V3 Plates good.
But... I have 160VDC on pins 3/8!
I should have 50VDC!?
Yes pin(s) 3/8 are tied to a 470 ohm.

I went forward with the instructions and set the bias
as instructed then installed the pwr tubes (Kt66) and plugged
a spkr cab in for load.
I tried to set bias and it doesn't seem to move much as
i sweep to mid pot. With all the controls off I got curious and
turned the volume pot up a little, with a guitar for source. it
made a loud mid to low sort of feedback which then went into
a sort of motorboating at about the same frequency as stated.
At htis point I didn't have a schematic so it was shot in the dark
and visual trouble shooting, Checking values and wiring connectivity etc.
I couldn't see anything unusual at this point.

I used the BOM, build insructions and pics provided.
I just found the offical schematic and will be using it,
(if I have time this wknd) to troubleshoot.

I appreciate any help suggestions ideas etc.

[neikeel]

Post clear well lit pics of your build and a full voltage chart, those are pretty much the minimum requirements for troubleshooting (at least for most of us normal mortals!)

[maxwedge572]

Are you sure you have a 470 ohm in there? What are your plate voltages for v3?

[?Mark]

Thanks for the replies.
V3 plates pin 1= 271 and pin6 266VDC respectively.

Yes 470 ohm in series with pins 3 & 8.

(I'd seen the post and reply to under voltage
problems on V3 pins 3 & 8 due to wrong
resistor value aka 470K ohm instead of the specified
470 ohm.)

I did look for answers in previous post but was
unable to find anything related to higher than expected VDC on V3 pins 3(8).

Spec for all preamp tubes calls out for 10% higher VDC than with
power tubes in but not 160 VDC on pin 3 & 8 THAT ANI'T NORMAL
Should have seen 50 or so.

I now have a good schematic and can now follow
thru while looking at the build. This will make life a lot easier.
This is the 1st chance I've had to sit down and reply, but no chance to
look the build over again. I will if time allows today.
Thanks again

[Elad E]

don't know about the voltage issue but regarding the motorboating - do you have swamp resistors installed?

[?Mark]

yes,
I have swamp resistors on both.