Cornet - Voltage Testing/Troubleshooting

Yoda · « **on:** 13 Feb 2005, 12:16 am »

Plugged in my cornet for the first time, and no smoke!

It works, sounds OK, but the voltages are all a bit low. Any help or suggestions would be great.

LOCATION....PRESCRIBED....ACTUAL
R107................365v............... .347v
R219L/R...........155v.............151v/151v
R212L/R...........150v.............136v/135v
R204L/R...........150v.............130v/129v
R211L/R(TOP)...330v.............316v/316v
R211L/R(BOT)...300v.............286v/286v

A few notes:
AC at my house is 117v, so I wired for 120v. Any harm in trying 110v settings?

I tested several 5y3, 5u4 rectifiers I had on hand, with similar results.

I am using Sovtek 12AX7LPS and an RCA 12AU7, stock components except for the recommended Auricap upgrades.

The sound is not as bright and focused as my preamp's built in, but I imagine this will improve with break in and normal voltages?

Thanks very much,

Matt

Eric H · « **Reply #1 on:** 13 Feb 2005, 01:20 am »

Hi Matt,

Congrats on your cornet! I must say I'm impressed that you managed to make the 2" deep Hammond chassis work. I tried that and ended up writing it off as practice and using a 3" deep chassis... got any pics? I put up a few pics of mine and detailed my experiences with the Hammond chassis in earlier threads...

I (and I think one or more others) have also noticed the voltages coming out lower than spec. I solved this by using a GZ34/5AR4 instead of a 5Y3. This brought mine right up to spec - I think I'm within a volt or two everywhere (I think I was 10-12 volts low in places). It's an acceptable replacement in terms of filament current, etc., too, and my PT barely gets warm. I'm using a Mullard and NEC (for my clarinet) that I happened to have (pricey) but you can get Chinese 5AR4's pretty cheap... I bought one recently but haven't tested it yet... there's supposed to be good, though.

Anyway... you're gonna love your cornet!
Eric

Eric H · « **Reply #2 on:** 13 Feb 2005, 01:23 am »

Oh, and one more thing - be careful with 5U4's... don't they have a higher filament current? Maybe the new beefier PT can handle it but I haven't checked...

hagtech · « **Reply #3 on:** 13 Feb 2005, 03:10 am »

Yeah, you'll have better luck with the 5AR4 or GZ34. Been using the Sovtek 5Y3 for production - it turns out to be indirectly heated and the supply voltages match the NOS GZ34 better.

Best place to check is the heater voltage. How close is it to 6.3V? That's the best indication of proper line voltage. I would NOT wire for 110V. Tube variation alone can push the plate nominals all over the place.

5U4 will work ok too. Tranny can handle it.

jh

Yoda · « **Reply #4 on:** 13 Feb 2005, 06:25 pm »

I have a Philips GZ32 that gets me closer. R107 is 355v now, R211 bot is 292v, but r212 and r204 are still in the 130's.

what points should I test for heater voltage?

what would be a good GZ34 to try?

I'll post some pics soon...

Matt

hagtech · « **Reply #5 on:** 13 Feb 2005, 10:29 pm »

You can measure heater voltage on the holes in the middle of the 9-pin sockets.

Remember, plate voltages do not have to be perfect. We are aiming for an operating region, not a specific 1% number. Each brand of tube will react slightly differently to the circuit.

jh

Yoda · « **Reply #6 on:** 14 Feb 2005, 05:27 am »

Jim,

The heater voltages measure 5.62 with a Sovtek 5y3gt, and 5.64 with a Dario Miniwatt GZ32, still a bit slight of 6.3v. How much of an issue is this?

Matt

Eric H · « **Reply #7 on:** 14 Feb 2005, 05:40 am »

Hi Matt,

For GZ34's the choices are old tubes like Mullards which are quite pricey (~$80 for NOS, maybe more?, but they last forever...) or recent production. Recent production GZ34's go for less than $20. I don't think there's much of a middle ground or any other tube rectifier with similar performance... Inspired by your questions I tried my Chinese GZ34 in my Clarinet last night and it worked fine, although I didn't measure the voltages (sourced from Jim McShane for $12 I think it was). I think JJ also made some GZ34's recently? No experience there...

Oh, and you say your cornet sounds "OK"... the sound of mine was all over the place for the first few days, and as Jim says the particular tubes you use can have a big effect on the operating points as well as sound... I've seen that with some of my old tubes. I'm pretty sure it'll settle down and sound great.... Eric

Yoda · « **Reply #8 on:** 16 Feb 2005, 04:42 pm »

My Cornet is really opening up and sounding great! It will be teething for some time, but already I can see that there is a lot of promise here. The bass response and smoothness compared to the SS board in my preamp is remarkable. While there is a lot of detail and crispness with the battery powered SS board that was lacking initially with the Cornet, I can already tell it will come into focus.

What I don't miss is some low level hash from my previous setup. The cornet is really quiet.

I am using a Shure V15VxMR cartridge, Rega RB-300 arm mounted on a tweaked Thorens TD160 with a custom armboard, and a Decware SE84CS-EX amp with homebuilt Decware HDT speakers. Oh--and the U.F.O.!

Yoda · « **Reply #9 on:** 18 Feb 2005, 04:51 pm »

UFO and Thorens TD160 w/ Rega RB-300 arm

Completed Cornet2 in 2" hammond case.

Eric H · « **Reply #10 on:** 18 Feb 2005, 07:17 pm »

Looks great! We must be reading the same forums or something, since my tt setup is essentially identical to yours except I have the RB-250 instead of the RB-300. Same cart, tweaked TD-160, custom built armboard. I plan to add a tecnoweight and experiment with different armboard materials pretty soon.

Yoda · « **Reply #11 on:** 10 Mar 2005, 03:13 pm »

M is for Mullard.....mmmm u l l a r d.

This is where the air is. Replacing the RCA 12au7 made an immediate difference...

Erik, anything to report on your Thorens tweaks?

Eric H · « **Reply #12 on:** 10 Mar 2005, 05:54 pm »

Well, since you ask... I got a Michell Tecnoweight yesterday. After only a couple hours of listening I'd say it's a nice improvement over the stock weight. I was expecting to notice changes mostly in the bass but instead I found that it improved the mids and highs a lot.... clearer and much more detailed. I'd guess this is because the weight is coupled directly to the stub whereas the stock weight is somewhat decoupled.

The weight is very nicely made but there was one surprise. In ads you'll see that it claims to offer 0.1 g adjustability. I thought this would be great with my V15VxMR - I could flip the brush down or up and quickly change the tracking force by 0.5 g. Not so... what they really mean is that you can set the tracking force with supposed 0.1 g accuracy without a stylus force gauge. To change the force you need to loosen an allen screw and move the counterweight, etc.... I'm happy with it anyway, though...