Epiphone Pacemaker 50T PT short

[angelodp]

At Edcor a standup, XPWR105 - 360V@250mA CT & 6.3V@3A.

I did talk to them and I don't see why this PT would not be just about right for this amp. What is lacking? It has the correct voltage with plenty of current capability and the 6.3v winding has 3A, more than enough to handle these tubes. Or am I missing something. Martin was suggesting two separate 6.3v windings but Steve showed an amp that did the deed on one winding.

[sluckey]

Given that what do you make of my selection at Edcor? It's between the unit that has two 6.3v windings and the unit with a single 6.3v and very close on the Secondary Voltage.

It's a push/pull 6AQ5 amp! And according to the schematic the power tubes are pulling 60mA. Add another 10mA for the rest of the amp. So, you need a B+ of 250VDC to 280VDC and about 70mA. Do your research based on that criteria and quit looking at all those big heavy transformers.

[maxkracht]

More HT current means your voltage will be higher when it isn't loaded down. How much, I don't know.

[angelodp]

Part of the criteria is the heater current at about 1.5Amps - Yes?

6X4 - 600ma
6AQ5 - 115ma peak cathode x2
6EU7 - 300ma x2


I wish the original PT was still avail, this is elusive.

[sluckey]

This is the PT I would buy for that little amp...

https://www.hammfg.com/files/parts/pdf/269EX.pdf

[angelodp]

Ok, you have never lead any of us astray..... done.

Thanks

[sluckey]

Part of the criteria is the heater current at about 1.5Amps - Yes?

6X4 - 300ma
6AQ5 - 115ma peak cathode x2
6EU7 - 300ma x2


I wish the original PT was still avail, this is elusive.

Those numbers mean nothing! Look at the schematic. The output tubes share a 270Ω cathode resistor and there is 16V across that resistor. That means the power tubes are pulling 16/270=59.25mA. Adding another 10mA for the rest of the amp circuit brings you up to 70mA required from the rectifier. That little Hammond PT I suggested would be very happy in this amp. No need for zeners, big droppers, etc.

[angelodp]

Ok, great, just deleted the Zeners from my order.

Thanks

[angelodp]

Just tested the old 6AQ5's on a rig I have and they are not doing great. One heated up a lot, compared to my usual 6AQ5 and the other one cut out after a bit. They are low cost tubes so I'll source new ones. I need to complete the replacement of the other electrolytic caps and look into the fusing Steve suggested. The 6X4 tested ok.

[sluckey]

Best place to buy Hammond transformers...

https://www.hawkusa.com/search?search=2 ... er_page=10

[angelodp]

Hey Guys, got that PT installed and amp lives again. Looking at maybe a bit of voicing with some suggested cap changes, C6 for .022 and pull C 13, not sure if hum is an issue have to get it in the cab, might swap C12 up to 47uf. Also order a fuse for the Sec CT, have to install.

Speaker has a few small 1/8 holes at the edge so I will attend to those.

Cheers A

[Stevem]

The largest input cap allowed by the tube spec for a 6x4 is 10 uf.

If the amp has a standby switch then stuffing a 47 in there will close to blow the 6x4 right away when you take the amp out of standby.

You might get by with 15uf, but still you would likely then have the life of that tube cut short by 50%.

If with only the output tubes in the amp you find a unacceptable level of 120 hz hum, then maybe your output tubes are too far unmatched to cancel 120 hz hum.



If you turn on the amp with no tubes in it and get 60hz hum out of the speaker then your OT is not in the ideal position to not have the 60 hz from the PT not couple into it.

In these cheap amps back then manufacturers did not care about details like that, so don’t drive yourself nuts trying to get perfection!

[Phil_S]

I'm late to the party, maybe too late. That Epi 50T is very similar to my Gibson Scout GA17-RVT, also PP 6AQ5. The schematic for the GA17-RVT says plate voltage is 300VDC. With today's wall voltage, IIRC, it is more like 315V. This amp has been in storage for about 10 years, so I'm not sure about a few things, but my recollection is that it was reasonably happy at 315V. I"m guessing it would be better at 300V. The yardstick for using a 6X4 says VDC is 1.1x input voltage. 300/1.1 = 272. FWIW, I agree with the suggestion for a 70mA 270-0-270 PT. As I recall, all of the iron in my amp is rather puny, but works just fine. Good luck with it, Ange.

[angelodp]

Hi, using 22uf 450v caps right now.I get 208VDC on the plates, both equal. Very low hum right now and it's not buttoned up. I have the PT at a diagonal position relative to the original so I could make the holes work. Seems to be fine. Let me add that I am at 115VAC on a Variac.

A

[angelodp]

Hi Guys, well damit I got covid and got bored so went to work on the rusty chassis. I reckon it would take many more hours (already have quite few in) than is called for....but it's an improvement. Almost buttoned up.

I need a suggestion for a speaker that would improve the overall dynamics, if that is even possible give the original intention. It's better served on HB's but hey maybe the right speaker could be interesting. Overall, even at lower plate voltage it sound very nice and trem is cool, no hum with hand on guitar. I need to put the final bottom plate on and that will help.

Thoughts - suggestions. 10"