Cornet transformer running very hot - any ideas?

troporobo · « **on:** 19 Feb 2006, 02:37 pm »

The Hammond 370BX on my recently completed Cornet runs very hot, in fact too hot to touch. This doesn't seem right. Everything else checks out all right. The only anomaly I can think of is that its wired for 220V but our supply is often at 230. Could this be a cause and if so should I rewire for 230V? Sorry if this has been covered before, my (cursory) search of the archives didn't turn up a clear answer through there were some suspicions in a few posts about rectifiers. Mine is a standard 5Y3. How could I check if this is causing the overheating? TIA

hagtech · « **Reply #1 on:** 19 Feb 2006, 10:46 pm »

Sounds a bit too hot. Trannys always run warm, but you should be able to hang onto it. I'd rewire it for 230V. Better to be on the safe side of things.

You can use a GZ34 type to raise B+ back up if necessary.

jh

troporobo · « **Reply #2 on:** 20 Feb 2006, 02:02 am »

Thanks Jim - will give that a try

Is it possible to guess what a 5AR4 would do, either before or after rewiring to 230? I read a few posts with that recommendation

Eric H · « **Reply #3 on:** 20 Feb 2006, 02:22 am »

I guess I'm the one that often mentions using GZ34's - they will usually give about 10V more B+ and are generally considered to be "better" rectifiers than 5Y3's... but check your voltages.

But I think you have a much more serious problem - if your PT is too hot to touch something is really wrong and I wouldn't run it that way. The PT's on my Cornet and Clarinet (370's) barely even get warm... easiest/safest tests are to run with different tubes or no tubes, and then (re)check wiring of course... be careful. Maybe you have a bad PT?

hagtech · « **Reply #4 on:** 20 Feb 2006, 04:50 am »

I'm sure the tranny is ok. Make sure it is wired correctly, and you'll be fine.

The thing with the 5Y3 - design was centered around the Sovtek 5Y3 new production, which happens to be indirectly heated! It also seems to act more like a 5AR4/GZ34 than a real 5Y3. So NOS 5AR4 work best as substitutes. 5Y3 has more voltage drop and results in a little softer sound, perhaps warmer. Not bad, just a little different. That's the beauty (and curse!) of rolling tubes. You can fine tune the sonics for your personal taste. You can make the Cornet aggressive or laid back, punchy or neutral, and can even tilt the tonal balance.

There is no magic combination that works for everyone. But certain trends are apparent. The X7s work the tone and smoothness. U7 the dynamics and slam. Y3 the weight of tone and bass. Tube dampers almost always help.

jh

SHIF · « **Reply #5 on:** 20 Feb 2006, 05:32 am »

“…The X7s work the tone and smoothness. U7 the dynamics and slam. Y3 the weight of tone and bass.”

This is an excellent explanation of the sonic merits of each valve. I’ve sorta figured most of this out myself through much tube rolling these past two years. I settled on a Raytheon 5Y3 rectifier and adjusted the value of the resistors to yield 330 volts on the downstream B+ rail. I want to try a vintage Mullard 5AR4 but can’t see paying the price these tubes fetch. I can pick up a bunch of LPs for the price of that Mullard.

However now I plan to purchase a Sovtek 5Y3 to hear my Cornet as Jim “voiced” it. I’ll again adjust the R2 resistors to achieve 330 volts.

Has anyone tried the Bendix 6106?

-S

GRD · « **Reply #6 on:** 21 Feb 2006, 05:15 pm »

Yes - I have tried a couple of the 6106 and a few 6087 (also indirectly heated 5Y3). The 6106 has very interesting construction - heater inside a ceramic tube and support rods everywhere. As for sound - it's a bit laid back/smooth. I also tried 5V4's which I found a bit too bright and aggressive (not as enjoyable). My favorite is the RCA 5Y3GT and in general any of the directly heated 5Y3 varieties. I was hoping the indirectly heated would be my perference as I would prefer the slower heat-up times. The 6106 takes over 30 seconds to come up. I never tried the Sovtek. Also never measured the voltage differences between rectifiers.

Hope this helps.

troporobo · « **Reply #7 on:** 21 Apr 2006, 05:01 am »

To address the problem of a very hot transformer I rewired the Cornet from 220V to 240V. This dropped all the voltages to about 5% below spec. However the transformer is still running very hot. I'm stumped! Any more ideas?

hagtech · « **Reply #8 on:** 21 Apr 2006, 06:54 am »

I'm stumped too. Have you looked at you ac line? Wonder if it contains a lot of harmonics, say has a squared off top?

jh

troporobo · « **Reply #9 on:** 21 Apr 2006, 08:14 am »

Sorry Jim, I have no way to check this, but will ask around locally and see if anyone can help me.

Meanwhile, everything is sounding very good and I'm very happy with the performance. I'm just worried about long-term damage if it keeps running like this.

By the way, I tried a NOS Mullard 5AR4 in place of the Sovtek 5Y3 and really like it. It produces a much smoother top end and more controlled bottom end, though also a slightly softer sound overall. The voltages are higher of course, by about 3-5% over spec, but I guess not enough to worry about.