Help Marshall vs65r

[nickb]

I think that's believable. Still pointing to the V1 stage as the problem. It would be handy to stick a spare 12AX7 (==ECC83) in right about now just to see what happens. It would not be the first cathode follower that I've seen fail due to excessively heater to cathode voltage. I recall you measured about 200V on the cathode (R19). The tube spec is 200V and some makes are better than others.

[AL78]

SO do I have to buy a new tube?How much is it?

[nickb]

I really don't know yet. We'll know more when the capacitor comes is. On the other hand do you know where you at least borrow one for a test?

Or buy one here https://www.thomann.de/it/jj_nn003_roehre_ecc83s.htm EU8.90 + shipping.

[AL78]

Unfortunately Nobody can lend me one.But as soon as we test with the cap(I should get this week)will see I've found this in italy ECC83S JJ-ELECTRONIC 12AX7 ECC83 tubes tube valvole NUOVA TESTATA | eBay
is it the right one?

[nickb]

I just checked the data sheet for the JJ's. The max heater to cathode voltage is 180V. Better go for a Sovtek 12AX7LPS ECC83 - 12AX7LPS SOVTEK VALVULA NUEVA NEW TUBE RÖHRE TESTED | eBay

[AL78]

Ok will see after the test.I'll call the owner when we are certain it's the tube.Have a good night

[AL78]

that's whats inside the amp now https://www.musicmaker.ie/amps/valve...low-microphony

[AL78]

Guys I didn't abandon you :-) The cap didn't come up this week I hope next week

[AL78]

so guys finally I got the cap so If i understand I need my "signal generator" to check if the tube works.So can you please tell what i have to measure now?

P.s. for nickb
Since you like etna yesterday there was an explosion and 10 skiers where lightly injured(nothing serious) :-)

[nickb]

so guys finally I got the cap so If i understand I need my "signal generator" to check if the tube works.So can you please tell what i have to measure now?

P.s. for nickb
Since you like etna yesterday there was an explosion and 10 skiers where lightly injured(nothing serious) :-)

And a bunch of journalists nearly died.

OK. Add the cap in series with your meter lead, either black or read it doesn't matter. Set up the signal generator test like before and measure the ACV at the junction of R9/R10, R20 where is connects to V1 anode & grid and R19 where is connects to V1 cathode. It would have been a big help if Marshall had bothered to put the pin numbers on the schematic for V1

[AL78]

Hi thanks so I put my signal to 300mv I get 2.195v on the junction of r9/r10

So If I understand right I have to check the 2 points where there is continuity with r19 right?
Both point is 86v AC

Unfortunately for r 20 there is more than one point of continuity how can identify the right one?

[nickb]

Hi thanks so I put my signal to 300mv I get 2.195v on the junction of r9/r10

So If I understand right I have to check the 2 points where there is continuity with r19 right?
Both point is 86v AC

I don't understand what you are saying. R19, R42 and R48 are all connected together so you should get the same 86V on each. Check that you do.

Unfortunately for r 20 there is more than one point of continuity how can identify the right one?

Doesn't matter any more since you have a signal on R19

[AL78]

This is what I did I check for continuity between r 19 and all the tube pin and i find out that there are 2 both pin have 86v AC that's what i meant

[AL78]

I was thinking does this mean that the tube is ok?what we do now?

[nickb]

Yes, the tube is OK. Do this, see #192 "R19, R42 and R48 are all connected together so you should get the same 86V on each. Check that you do."