What causes this?

[Steve Conner]

I'd still like to know what heater voltage he gets with *all* the tubes (both pre and power) removed. If it's like 7V then the tranny is surely getting overloaded. If it's only 6.5 then it's just a case of low line voltage rather than overloading, so the tranny is one of those ones that just runs hot anyway.

One thing I thought of: Is the tranny one of the new style international ones that has two 120V windings? You're supposed to connect them in series for 240V countries and in parallel for 120V. If you just hooked one of them up to 120V, that might explain the hot running and low voltages, since the primary is getting hit with twice the current it's designed for.

EL34s can be a pain, they draw about twice as much heater current as anything else save for KT88s and 6550s.

PS: oops my mistake on the preamp heater currents :|

[stokes]

I think all the voltages would be off by a lot more if it were the 240/120 problem you describe,although I must say I have never actually played with an import tranny.I think this has come down to either the tranny just isnt really rated for the stated 7amps,it was defective out of the box or from drawing the extra .3amps it has already started to deteriorate,which would be doubtful unless it is a real piece of crap tranny.But with all the preamp tubes pulled and the power tubes only drawing 6 amps and still not getting 6.3 or better,I think it is only logical that the tranny is history,and adding an aux heater with this one is not practical.Trying to use a part that is known to be defective can only get you in trouble later.

[496dart]

Well guys, im calling Antique on Thursday and see what they think. I hope they will replace the trans. I really doubt it though...

[496dart]

They said to send the old one in and a new one is on the way. I will keep you posted......

[stokes]

When you get the new one test it with no tubes,you should get close to 7vac.If you do, first install the power tubes,if you are getting 6.3vac with power tubes,install the preamp tubes one at a time and monitor the volts.If the volts drop below 6.3v then the amperage rating is over stated.In this case an aux filiment tranny would be the answer.By the fact that they are willing to replace it tells me the one you have is defective and you should be okay with the new one.They can tell by the symptoms this is the case and have confidence a new one will perform as advertised.

[496dart]

got the new one. Here's the latest:

No tubes in-

power socket:
1 6.60 v
2 6,58
3 6.56
4 6.54

PRE sockets
1 (PI) 6.53
2 6.52
3 6.51
4 6.51

Next installed 2 different sets of power tubes (with no pre-tubes):
power tube socket 1 , 6.12v
2. 6.07
3. 6.03
4. 6.00

B+ with tubes in is 460v, plates are 459v

right now ive got it idling to see if it gets hot


so what do you recommend for an aux trans ? and this would just drive the power tube filimants?

EDIT--of course--it got hot after an hour.

[stokes]

Something aint right.When you install the power tubes your heater winding is being overloaded.Try it with just the preamp tubes and see if it gives you 6.3 volts.If that is a 7amp heater winding ,the power tubes are only 6amps the volts should not drop that low.See how it holds up with just the preamp tubes.

[496dart]

With only the pre tubes: 6.60 v

[stokes]

The volts are okay with just the preamp tubes.Before we get into the aux tranny,pull all the tubes and check the resistance to ground at all the heater pins.Do this with the heater CT connected to ground and without.With it grounded you should see 0 ohms,with it lifted you should not see any resistance to ground it should read open,dont confuse the heater CT with the high voltage windings CT.I believe you said the heater CT is green and the other is yellow.Dont connect the high voltage CT to ground,with that rectifier it will blow the fuse if it is.Also make sure the heat issue is gone with only the preamp tubes installed,once we make sure of all this we will talk about an aux heater tranny for the power tubes.

[496dart]

the trans does not get hot with just the pre tubes.
resistance with ct grounded was 0.8 ohms . with ground lifted, inf.

[stokes]

I would suggest disconnecting the power tubes heaters and running them on an aux.6.3 at 7 to 10amp.tranny.That main tranny you got cant be 7amps if it cant run the power tubes.That is without a doubt the cause of the overheating and subsequent burning out of the main tranny.It should be fine just running the preamp tubes.

[Steve Conner]

Arg, that voltage is sagging badly What gauge of wire did you use for the heater wiring?

[496dart]

ok, ill order one tonight.

Steve , the wiring is the same as any other amp . 16- 18 ga. ? dont remember the exact #.

[stokes]

I dont think the wire gauge would have anything to do with it,if the wire were to thin it would burn up.You did say you tried a different set of power tubes,right?If some internal element was shorting to your heater element in the power tube,I am pretty sure it would blow a fuse,never seen it do otherwise,just wondering if for some reason your power tubes are drawing more than their rated 6 amps,this would be very odd if they did,so the likely hood of two different sets of tubes exhibiting this oddity would be slim to none.I know we've been all over this but just give another check to be sure nothing is connected to that heater supply that shouldnt be.It doesnt make sense that they would understate the amps on that heater,but the odds of getting 3 trannies in a row that have the same problem is unusual,and the only other possibility is that the heater does not actually have a 7amp rating.It is fine with just the preamp tubes,so the aux tranny will work.Just make sure you get at least a 7amp and 10 would be better.Let us know if you need any help getting it wired in.Pretty basic,your primaries hook up just like the main one to the switch,one to the fuse,and the secondary goes to the power tubes heaters.Just be sure to seperate the pre from the power tubes heaters.

[Steve Conner]

Well, thin wire can cause a voltage drop without getting so hot that it burns up. But 18AWG should be plenty thick enough, even if all the heater current flowed through a single pair. I guess it does sound like the transformer is underrated.