Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Leevi on August 07, 2011, 04:23:26 pm
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What are the specs of the 5E5A PT?
If I'll use some other type of PT do you recommend that the PT has higher or lower voltage secondary?
Do you think a Marshall 50W OT (3800 Ohm primary) would work fine?
/Leevi
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Power-wise, this IS a 5F6-A Bassman, so use standard "40W-50W" Fender replacement iron.
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If I had to use some other PT, I'd shoot for slightly lower voltage. That's because either the wall voltage is a bit high, or the transformers tend to have extra current reserve, and the secondary voltage winds up higher than expected/calculated.
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...so use standard "40W-50W" Fender replacement iron.
For the PT great but I don't like the Fender OT's that force you to use 2ohm output taps.
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the pt# for a mercury magnetics 5E5-A PT is FTWPRO-P
should be 330-0-330 secondaries plate voltage with 6l6GB's should be about 385VDC
5V@3A rectifier
6.3V@6A heater windings
45V bias tap
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for the OT use doug's 40W universal pro reverb / super reverb / bassman / bandmaster replacement - has 2-4-8 ohm taps. excellent stuff.
Part number 018343
for the PT use the bassman / super reverb PT.
Part number 022798
--DL
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should be 330-0-330 secondaries plate voltage with 6l6GB's should be about 385VDC
I think with 330v secondary the voltage will be too high.
This is of course depending on the PT and rectifier and filtering.
I'm now looking for a PT with 300-0-300 secondary.
/Leevi
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with a 5U4GB your plate voltage should be around 385VDC with 117VAC on the primaries. That is what I'm getting.
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Yes.The 330v will be fine with a 5U4 rectifier.The 300v will sound great too if you are worried about voltage.It's not likely you will be using 6L6GB tubes but rather 6L6GC's anyway so it won't be an issue.
Are you using a Fender style chassis or one you are making?Hammond's 300 series transformers have a nice 300v primary with European voltage taps,5v taps,and a bias tap too.Big and heavy though.I actually pulled the bell cover off one side of one of those and installed it into a Fender Super Reverb chassis.That was 5 years ago and it's still working fine.It has a few voltage options too so you can fine tune it for any voltage requirements.
I also think the Guitar line has Euro-spec voltage taps now too.
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I have been quite often disappointed with too high DC voltages that should have been lower.
It depends very much on the PT manufacturer.
I built couple of years ago a Marshall Plexi where I first used a PT which was made by a small Finnish company:
The secondary was 345-0-345. I measured 480V B+ with idle load.
I changed the PT later to Hammond 290GX where the secondary was also 345-0-345 but the B+ with idle load
was only 420V. 60 Volts difference!
The 230V primary shouldn't affect? 50Hz vs. 60Hz?
Are you using a Fender style chassis or one you are making?
Yes, Fender steel chassis or a copy of it (I'm not sure)
Hammond's 300 series transformers have a nice 300v primary with European voltage taps,5v taps,and a bias tap too
I'm going to use Hammond 302AX 300-0-300/230mA, 50, 5, 6.3
It has a few voltage options too so you can fine tune it for any voltage requirements.
Yes
/Leevi
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The wall voltage in European counties is a huge factor.I built a couple of backpack sized amps that a band toured Europe and Asia with.They had voltage surges and anomalies in some countries and not in others.Luckily I used Hammond PT's and lower voltages overall.
No failures to date after 5 years.
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I started the project and the first voltage measurements have been done.
All tubes are in place, heaters are connected also power tube plates and OT.
The plate voltage is currently 430V. It will probably drop when I get the power tubes biased.
I'm using Hammond 302AX where the secondary is 300-0-300.
/Leevi
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sim shows 415V to plates with a nominal load - 66mA or 33mA/6L6GB, ~14W @ ~70% of 19W max Pdiss., G2 load @ 4.5mA, rest @ 8.5mA
transformer = 325-0-325 @ 230mA - hammond replacement 290DX, 5U4GA recto, 110ohm 4H choke.
A = 415V
B = 410V
C = 325V et-al
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I got the amp wired and have measured the voltages under operation.
The Hammond 302AX gives possibility to set the PT primary from 100VAC to 240VAC.
The nominal wall voltage is here 230VAC. The 302AX secondary is 300-0-300.
I tried both with 240 and 220 primary settings (I'm not sure if it's allowed to set the 230 since
there were not instructions for that?)
B+ with 240 and 47mA cathode current is 360VDC
B+ with 220 and 47mA cathode current is 393VDC
/Leevi