Another finished Cornet, break-in time?

Braden · « **Reply #20 on:** 8 Oct 2003, 09:37 pm »

Can I test the transformer wires while they're attached to the board? All of the wires, the green, yellow, and red all read 22v on the meter. This can't be right. Would the transformer act like this if it's pooped out?

penance · « **Reply #21 on:** 9 Oct 2003, 07:07 am »

HI Braden

I think if you go to the Hammond website and search for the 270BX(or 370 if thats what you used) they have a diagram showing the leadout and expected voltage.
Check for any obvious bad joint or burn tracks on the PCB, im no valve expert but i suspect if the 5Y** tube is shot then that may stop others working.

Braden · « **Reply #22 on:** 9 Oct 2003, 03:06 pm »

Penance,

I thought that it might be the 5y3gt tube, so I switched it with another one, and nothing happened. I left the black wires connected to power, then removed the green, yellow, and red wires from the board and measured them. They all read about 13 volts. I then removed the transformer from the chasis. There was a yellow stain below the transformer on the chasis, and it smells like burnt electronics, which can't be good. It seems the most likely culprit. Especially because I didn't have the fuse wired in at the time to protect it. It's expensive, but I guess I'll have to order a new one.
Hmmph,

Braden

penance · « **Reply #23 on:** 9 Oct 2003, 03:39 pm »

the yellow stuff sounds like burnt varnish
that would point to the Tx haveing been overheated

Braden · « **Reply #24 on:** 9 Oct 2003, 05:45 pm »

Penance,

Well, I'll find out tomorrow if it's the transformer, which I'm sure it is. When it first burnt out it left a nice yellow stain on my carpet because I had it sitting on the floor. Live and learn, live and learn.

hagtech · « **Reply #25 on:** 9 Oct 2003, 06:05 pm »

Everyone, thanks for the help while I was away. Here's my guess at what happened...

Maybe C9 went bad. If so, it shorted, which then caused R20 to sit across the B+ windings. That would overload the transformer and immedaitely blow the fuse. But the fuse was not in circuit? That caused the tranny and R20 to overheat. Fuse should have protected the tranny.

R20 is just part of a snubber network to damp tranformer ringing caused by the switching of the rectifiers. Circuit will run fine without it.

As for burn-in, I'm not sure what a super-high input signal level will do. Certainly sound like a guitar amplifier. Burn-in should be done using an iRIAA filter, which corrects for frequency compensation and signal level.

I'm a little suprised we have two failed Hammond 270BX at the same time. I have not had one fail yet. These are the first two I know of. Normally, they run quite hot, but that is fine. They are designed that way. However, it helps to have good ventilation. Mounting the transformer on top of the chassis is good. If it is buried inside, then you need to insure adequate ventilation.

jh

Braden · « **Reply #26 on:** 14 Oct 2003, 05:20 pm »

With regards to breaking in the Cornet, I remembered I had a record in my collection that contains 500 lock-grooves. So I can leave it running while I'm at work. My cartridge is about 5 years old now, so I'm not too worried about putting the extra miles on it.

Braden