Just installed a replacement power trannie in my 5E3 (Thanks Ted Weber!) however I'm seeing something I wouldn't expect.
I'm using a light bulb limiter (25W globe) and the bulb is glowing (but not brightly) with no tubes and no 6.3V bezel installed! The amp is NOT blowing fuses and appears to be working fine (if not better than before). The replacement trannie is bigger than the original by ~20%.
Is what I'm seeing normal? My expectation is no current would be drawn when the trannies's outputs are all open circuit. Could leakage flux cause this? Can't find a short anywhere!
BTW I feel really dumb asking this questions after working with electronics for 35 years - but there you go - help!
Thats a good one .... the current has got to be goin some where..... Ive seen a few hopeless fender power trannies.... would suspect its wire coating broken and shorted or paper between windings.... any thing from mold to moisture .... in an old tranny that is.... could be the spec of the tranny yours was modeled on....contact the maker
So your saying there's no load on PT secondaries? Are they wired up or tapped off? Does it blow fuse with current limiter disconnected? Shorted PT won't blow fuse if current limiter connected and no load.
tonelab2 wrote:So your saying there's no load on PT secondaries? Are they wired up or tapped off? Does it blow fuse with current limiter disconnected? Shorted PT won't blow fuse if current limiter connected and no load.
Correct, no load (which is why I'm confused!)
Unused leads are cut short and have heat shrink on their ends.
Andy Le Blanc wrote:Thats a good one .... the current has got to be goin some where..... Ive seen a few hopeless fender power trannies.... would suspect its wire coating broken and shorted or paper between windings.... any thing from mold to moisture .... in an old tranny that is.... could be the spec of the tranny yours was modeled on....contact the maker
No this is a *new* Weber Trannie (replacing an old Weber trannie). Like I say above - this trannie seems about 20% bigger than the original.
Don't think there's any mold or moisture involved and yes its for a 5E3 clone.
Given its a 25W bulb the current wouldn't have to be that high to light it.
(gets out envelope) Say 25% or 6watts - thats 6W/240V = 25mA
Still scratching head though
Edit: OK I should measure this leakage properly - will check again tomorrow.
Even an unloaded transformer has resistance and inductance, and this will still form a (lighter than normal) load in series with the light bulb. Does the amp have the normal Fender-style 100R 'virtual center tap' resistors on the heater winding?
mhuss wrote:Even an unloaded transformer has resistance and inductance, and this will still form a (lighter than normal) load in series with the light bulb. Does the amp have the normal Fender-style 100R 'virtual center tap' resistors on the heater winding?
--mark
Good one Mark. Also, 270K bleeders on filter caps?
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mhuss wrote:Even an unloaded transformer has resistance and inductance, and this will still form a (lighter than normal) load in series with the light bulb. Does the amp have the normal Fender-style 100R 'virtual center tap' resistors on the heater winding?
--mark
Thanks Mark,
No virtual CT - I'm using an actual CT on the 6.3 winding.
The 5E3 stock circuit simply grounds one side of the 6.3 so I don't know what you mean by "normal Fender-style 100R 'virtual center tap'" at least in the context of a 5E3.
Progress so far: well... none, but...
... I hooked up my Lightning clone minus tubes and bezel and sure enough there was some current drawn. So panic has subsided - although the 5E3 draws more current.
Interestingly the 15W Lightning is MUCH louder than the 25W 5E3 (through the same speaker no less!). The Lightning uses WestLabs trannies while the 5E3 uses Weber PT/OT. However the 5E3 is MUCH sweeter sounding. The Lightning sounds good but more the stock AC30 clang clang ker-chang. Just a observations and more head scratching
Do you mean by that no tubes in sockets and no indicator bezel light?
If so, I suspect there's still plenty of scope for DC leakage through supply decoupling and filter caps, etc. It will all add up.
Even if ALL secondaries are fully disconnected the primary is in effect an inductor and a resistance is series, it will draw some current too.
How much current in each of above cases is unknown to me.
I note disconnected wall warts get quite warm.
Ears wrote:It isn't clear to me what you mean by unloaded.
Do you mean by that no tubes in sockets and no indicator bezel light?
If so, I suspect there's still plenty of scope for DC leakage through supply decoupling and filter caps, etc. It will all add up.
Hey Ears - yes unloaded is as you describe but, since there's a tube rectifier, with all tubes pulled there's no path through filter caps or bleed resistor to ground.
Yep - seems it does add up - to about 10-30mA!
Guess I'm just surprised either:
- so much current leaks through the trannie on it's lonesome
- so little current is needed to light a 25W bulb!
