2 el84 rocket

[mark enger]

Would i want to run el84s @ 250 plate voltage or closer to 18watt marshall voltages?

[M Fowler]

Mark that depends on what your PT secondary puts out. Typical 18w Rocket transformer I used had either 260v or 290v.

Rocket expected voltage using 250v is 285v on plates. I used 290v so got 347v on the plates.

I would use the lower secondary 250v to 280v range. But your right it can get very similar to an 18w Marshall voltages.

Mark F.

[rawnster]

I just put together a (15 watter)british style amp using MM AC-15 tranny set. It sounds extremely nice. Yet the voltages are high. About 386VDC at the reservoir capacitor, and about 382VDC on the EL-84 plates. Hmmm, hasn't blown up yet. Those russion saratov tubes are truly nuclear grade!

[surfsup]

Rawnster, may i ask what your screens are at?

[mark enger]

The reason i ask is i have a few powertranys that measured like 275-ct-275 no load so i thught id build a 18 watt lite with ss recto, figureing id be at about 300v on el84, i was getting more like 250 to 275 pate voltage and the 18watter sounded likda farty, so if these tw amps are designed at 250 platevoltage i thought id givem a try in a wrek circuit, i was also thinking of mismatching output transformer like a spitfire and run a small 4k ot, its just a thought while im collecting up parts for a rocket clone

[rawnster]

Rawnster, may i ask what your screens are at?

around 379, 380

[mark enger]

I have a few pt in the 275 unloaded range they came from pp 6v6 record players amps (webcors), and had very low plate voltage, that will give me somewhere in the 250 platevoltage range on the el84, Seems that KF designed these amps for lower plate voltage which must be part of there charm, Then i messed the drilling up on my rocket chassis making the pi tube to close to the powertube holes so its a perfect excuse to try a 2 holer, not sure about choke speck and will most likely skip it and use a resistor, not sure of ot even though 8k seems the norm for a 2 hole wrek, im gonna try 4k, 6k, 6.6k as i have surplus of them, im finshing up a 6v6 18watt marshall now then ill try the 2 hole wrek, and by then i should be ready to try the rocket clone, I was also considering a 5 watt wrek with some ell80 i have there duel pentiodes in a single bottle i did a 5 watt marshall lite and the tube worked out great, was also thinking 6aq5 wrek?

[rooster]

Hm. I used an MCI Marshall style 18 watter PT. Unloaded, the PT read 311-0-311 VAC. With the circuit built, using a GZ34, I read 371 VDC on the first stage PS cap.

[rawnster]

Hey Rooster, similar readings... the build I mentioned earlier uses a PT that reads 330-0-330. After built using an EZ81 recto, I get about 386 on the first filter stage...then going to the second filtersection via a 10 henry/100mA choke, it reads about 379VDC. This 379 feeds the powertubes.

[rawnster]

I replaced the 100ohm screen resistors with 1k. Brought the voltage down a few volts (375 range). I should probably swap out this PT for something rated a little lower, but dang there's something really cool sounding about this particular build. I'm very hesitant to change anything. Tubes are cheap, right?