JTM 45 fixed!

[Reeltarded]

Bad 150k bias resistor!!! MY BOAT HAS BEEN IMPOUNDED!



3 mistcakes on this board. I wonder how many people got the same thing from the last run of Metro BBRI boards.

Output is low. Gain is minimal. I have some things to work out but not in the PS anymore. I can tell this amp is going to be quiet at idle. Still not biased. Need to recheck all the voltages and maybe dump that 8.2k at the bottom of the 10k.

I saw a big flash from the GZ34 last night before bed. Do you think it's a goner?

Thanks guys! The moral support is everything, the thinking help is invaluable.

[Firestorm]

Bad 150k bias resistor!!! MY BOAT HAS BEEN IMPOUNDED!



3 mistcakes on this board. I wonder how many people got the same thing from the last run of Metro BBRI boards.

Output is low. Gain is minimal. I have some things to work out but not in the PS anymore. I can tell this amp is going to be quiet at idle. Still not biased. Need to recheck all the voltages and maybe dump that 8.2k at the bottom of the 10k.

I saw a big flash from the GZ34 last night before bed. Do you think it's a goner?

Thanks guys! The moral support is everything, the thinking help is invaluable.

Russian GZ34 or Mullard? Takes a big short to kill a Mullard. But once they arc they wil do it again. You should power up with a different rectifier to be safe. There's really no way to test a rectifier tube for shorts at full voltage except to look for fireworks.

[Reeltarded]

Ok, so got good signal injected. Same rectifier tube (JJ GZ) though.

Turned it up with expected results to about 4 and it started sputtering and thuddy like motorboating but faster. Turned it off. Back on the bench. I can't be far from getting this straight. I am a little wary of using the last 2 rectifier tubes I have on-site.. if I drive to where the other stuff is I have to take 2 Fenders apart so I can get you gutshots. lol -that I haven't forgotten about btw)

[cbass]

You can put some diodes across the rectifier socket and go ss till you get a good gz34

[Bob S]

Good Luck - I'm sure I'm not alone letting the black belts help with the birth.
Won't be long now - a smack on the backside & it'll be screaming.
In a good way.

[Reeltarded]

Oh my lord. Swapped the JJ for a known POS Chinese 80s GZ that works and started measuring.

DOOD 452 @ the plates!! That is what I am used to on JMP with SS rec.

That tube rattles. I am going to swap back for a minute and see what happens.

Ok NUTS! 452 plate volts. And I thought this monkey was going to be around 400. Holy chicken schmidt.

On pins 4 and 6 of rectifier the readings are +2 something to - 1 something that changes too fast in a sweep for my meter to keep up.

What does that mean? heh

Bias V4: -36 Bias V5: -60 yerkeses..

[martin manning]

On pins 4 and 6 of rectifier the readings are +2 something to - 1 something that changes too fast in a sweep for my meter to keep up. What does that mean?

Not trying to measure DC there are you?

[cbass]

So you are saying that pin 5 on v5 is -60? That's why your voltage is way high that tube is not drawing any current.Don't know why they are so different though

[Reeltarded]

Anyone have a picture showing orientation of diodes on a rectifier socket?

Are the 1N4007 appropriate? What spec do I need? Radio Shack is my master, I shall want and want.

[Reeltarded]

On pins 4 and 6 of rectifier the readings are +2 something to - 1 something that changes too fast in a sweep for my meter to keep up. What does that mean?

Not trying to measure DC there are you?

Nope. I was trying for ac, but never ever considered my meter was trying to autorange. I will lock it and check again. I am flustered.

I hope there isn't something ugly in the bias section from the gank resistor earlier.

Yeah Ceeb. No idea why the one is so crazy far from the other. I am about to swap and test again. HAWT.

[martin manning]

Anyone have a picture showing orientation of diodes on a rectifier socket?

Are the 1N4007 appropriate? What spec do I need? Radio Shack is my master, I shall want and want.

Yes, 1N4007 is fine. One from pin 4 to pin 8, and one from pin 6 to pin 8, banded ends go to pin 8.

[Reeltarded]

GZ34: 2 and 8: 373v
4 and 6: 332v

I swapped positions with the 34s. The bias difference followed the tube.

2 of 10 bad JJs. All the luck! (Or at least 80%) scared to throw good tubes at it though. RFTs on the block.. uhhg my favorite pair.

[Reeltarded]

My methods are mixed and worse. Neg 38mA v4, Neg 16mA v5.

RFTs matched super bigtime. It's about the bias circuit.

[cbass]

I'd be looking at the coupling caps before your output tubes.

[Reeltarded]

Same feed though. How could it be so imbalanced if it were not simply a problem at the socket. Just looking at the schematic. It has to be my fault.