Checking current

[stokes]

While you have the tubes in you might want to check the current draw on the power tubes,I think,if I remember correctly,things are getting hazy with all the info we've been throwing around,you were drawing in the area of 88ma's.With the meter set to measure ma's put the red lead on your OT CT and the black lead on pin 3 of one power tube and see what we got.If you are reading over 30ma's we have to address that.

[MWJB]

You are UNDOUBTEDLY going to get a reading of over 30mA's with a stock 5E3, running a 250 or 270ohm cathode resistor and 370v or more B+. Run plate voltage, plate current and cathode voltage by us before you take any action on this front.

I would expect your current to be around 35-40mA per tube (normal current range for a 5E3), if it's higher than 40mA try a 330ohm cathode resistor. This will push up B+ voltages but should reduce overall plate dissipation slightly.

[The Captain]

Im waiting on those replacement spragues- Id post up current current, but temp caps are 450v so my knees would be knocking if 520v are flying about.

So another course of opinion it seems, notably the idea maybe 40-43mA is not quite so alarming, caps poss ok so try increacing the bias R to 330r- to my original course/ Mr. Stokes' idea that caps most probably cause for a defo alarming current drop/ amp heat shinanigans; a little tricky to know for sure where to go.. such is nature of forums I guess.

[stokes]

I was basing that 30ma's on you saying you have 500+v's with no tubes,and estimating that with the tubes in you are still going to have 400+'s.In a normal 5E3 35+ma's would be okay,but that would be if you had under 400v's on those plates,with over 400v's you would not want to see to much more than 30ma's.Class A with a pair of 6V6's at 400v's would be about 30ma's.

[Bruce / Mission Amps]

With correct primary voltages applied, most 5E3 plate voltages (with respect to ground) are around 350vdc to 365vdc and the power tubes idling mildly hot at around 36ma-40ma.

[The Captain]

Having a word with Weber giving Vs and current, they just said.. 'use the red/whites instead'.. these secondaries are 540v/? as oppsed to 640v/150mA between the 2 reds used as per normal on layout.

Are these usually used for a different amp? meaning I'll get significantly lower B+ ? Im not sure if thats good, bad or what.. Im still no closer to getting the amp as is solved whatsoever!

[MWJB]

640VAC (red wires) should give you spot on 5E3 rectified B+ voltages.

540VAC (red/white wires) will give towards the low side of 5E3 voltages even if you use a GZ34 instead of a 5Y3.

Sounds like you either have the wrong PT or have connected the wrong primaries?

[Bruce / Mission Amps]

The Chinese made Weber W25130 power transformer is a loose version of my old American made TMI 20 watt PT.
My TMI PT is a loose version of a silver face Deluxe Reverb PT.
However, my TMI PT had two different high voltage taps.
The 275vac secondary for my EL84 Crusader amps or higher 340vac secondaries for my 6V6 Crusader amp and a low power 6L6 amp I was building.
I don't use TMI anymore but my new USA made MA20/18 power transformer is very similar to my old TMI PT.
The 6V6 secondary is now voltage tweaked for the 5E3 kits when using a real NOS 5Y3GT rectifier but works great with a GZ30 or GZ34 in the 6V6 Aurora amp.
Side note:
When helping Weber with their transformers a few years ago I suggested he have his Chinese winder copy the specs of my Chicago made TMI power transformer.
I dont know if the more recent W25130 PT is differrent now, but at the time, the Chinese Winder (or maybe it was Weber) called it a 150ma PT (I doubt it) while mine was rated at +120ma.
However, I beta tested both the Chinese Weber PT with my TMI PT in a test jig I invented, which included loading the filament supply leads down to their current rating. I took these trannys right to the point of near meltdown.
I ran the high voltage secondaries at 80ma for 24 hours, 120ma at 12 hours, and for 2 solid hours at 150ma!
The Chinese one got scarey hot... smelly hot, feel it on your face hot....hotter then the hubs of hell!
My TMI got very warm too but not like the Chinese one.
Regardless, neither PT gave up the ghost in what was an extreme two hour, near total destruction test.
What I found was, at the same secondary loads my TMI PT could handle the same secondary currents but with less heat for some reason.... maybe TMI was more conservative and mine is +150ma too... based on some "Chinese duty cycle" rating. Ha ha...

[The Captain]

I have the reds connected ok, always did.. just Weber succinctly(!) just said.. 'use the 540v red/whites instead'. Even more confused now, I think I'll just have to live with a hot PT until it dies, then just shelve this amp.

[MWJB]

OK, so long as your heater voltages are 7VAC or under and over 6.2VAC (important, confirm this) and your B+ is under say 385v with a 270ohm cathode resistor, or under 420v with a 330ohm cathode resistor, WITH EITHER pair of B+ secondaries you will be OK.

If, with the 540VAC secondaries you only get 300-320vdc recitified (with 270ohm cathode resistor), that's not going to really be a problem (it would be nice to have over 30mA on the 6V6s), you can always use a stiffer rectifier to bump up the B+ *if you want*, OR try a smaller cathode resistor like 165-200ohms (don't do both). If the amp is just for home use, the lower B+ might even be in your favour, even try some 6K6s to drop power slightly?

PT heat - You have told Ted Weber what B+ you have with the replacement PT but I couldn't find a note in the previous posts (apologies if it's in there) so it's not easy to determine whether your high PT temp is solely due to the PT itself (wrong part/primaries) or an indirect symptom like very high plate currents due to raised B+. In any case some PTs do run "burn yourself after 20mins" hot under normal operation, as Bruce intimated. What you consider "hot" and what your PT considers a regular day in the office might be the same thing. On the other hand you could be right and the PT might be a problem...so just keep playing it and IF it dies you were right. It only takes an hour tops to chuck in a new one and you are now well versed in how to do it :-)

Building amps (especially 5E3s) isn't as easy as "put tab A into slot B", a lot guys get lucky...a good proportion don't. That's why kits like Bruce's Mission kits sell well (proven parts, construction methods, instructions and support) and cost more than other bare bones kits. You have jumped in at the deep end and you're probably swimming better than you think, but with limited experience it's difficult to determine with which components your problems lie, if there is a component issue at all - things like that only come with experience.

Now stop that silly "sheve it" defeatist talk, connect up the 540VAC taps (be aware that this is a nominal voltage, once you allow for manufacturing tolerances and 240v operation the reality might be quite different) and tell us what you've got. You're in danger of snatching defeat from the jaws of victory (I might have said that before? Well, everyone has to have a catchphrase.)

Good luck & chin up.

[The Captain]

Thanks for that info- I will try the other wires instead as a last resort. Its started blowing fuses again so Im defeated now Im afraid.

Thanks to all for help though- especially Mr. Stokes!
Captain

[stokes]

As we have all said,stick with it Capn,you got a lot of good people behind you,we'll have none of that "shelving" talk.I have been away for a few days,so I have to do some reading to catch up on where we are at here.

[The Captain]

I really am at my wits end now Mr. Stokes.. I need therapy again.. board's out now but the bits seem to be just laughing at me. Wiring checked THOUGHRALLY for the *th time- ALL good.

Q- if I had old or dried out 2x 0.1uf caps, could they lead to that mild distorty ghosty sound, or even this hot PT/ fuse popping piffle? Capt

[MWJB]

Re. the .1uf caps. Desolder the ends farthest from the plates resistors (or cathode @ V2,8), connect your red meter lead to the free end of the cap (making sure the free end can't short to ground), the black lead to the chassis. Measure the DC voltage leaking through the cap, replace if over 0.1v.

Having said that, did you get these noises with these caps and the old PT?

I wouldn't go changing anything else until you have the lower voltage secondaries wired up and confirm voltages/currents.

[The Captain]

No didn't get thse noises with old PT (same caps).

I hooked up the other red/white secondaries ('540v').. no sound at all, just background murmurs. Desoldered, resoldered, checked pins 4 & 6 recto.. same. Im nervous about even turning the amp on now.