250-0-250 for an AC30 PT?

[dehughes]

Totally, RJ sells an Edcor EM0727

260-0-260 250mA
6.3V CT 4.8A
5V 3A

http://www.rjguitars.net/Transformers.html

Very true...but I need a lay-down mount, as I have a nice big square hole in my chassis.

[RJ Guitars]

Hey guys,

The Trainwreck Rocket aka the Top Boost channel of an AC-30 is a low voltage outfit, so the history is there for sure. The Heyboer HTS-9144 is 250-0-250, and I also have the Edcor EM0708 at 245-0-245. This is what I use in my Rocket builds.

BTW be careful with the Edcor voltage ratings because they are loaded values and they tend to show 10% higher in the secondary voltage until you have them at their loaded current rating.

...but this laydown feature makes it all a bit more complicated. I dunno if anyone has a laydown with the right specs?

rj

[dehughes]

Hey guys,

The Trainwreck Rocket aka the Top Boost channel of an AC-30 is a low voltage outfit, so the history is there for sure. The Heyboer HTS-9144 is 250-0-250, and I also have the Edcor EM0708 at 245-0-245. This is what I use in my Rocket builds.

BTW be careful with the Edcor voltage ratings because they are loaded values and they tend to show 10% higher in the secondary voltage until you have them at their loaded current rating.

...but this laydown feature makes it all a bit more complicated. I dunno if anyone has a laydown with the right specs?

rj

Thanks RJ.....much appreciated. I can get the same specs in lay-down mount via Heyboer, so I'm good either way.

So, what would you think, in your experience, one can expect to see on the plates of a quad of EL84s with a 62ohm Rk, given your Edcor 250-0-250 PT with a GZ34?

[RJ Guitars]

....So, what would you think, in your experience, one can expect to see on the plates of a quad of EL84s with a 62ohm Rk, given your Edcor 250-0-250 PT with a GZ34?

After thinking about it for just a second, I think Gary Hultgren put together an extensive collection of voltages in various Rocket builds and that thread should still be available.

I did build a Rocket with a set of replacement VOX transformers one time and I found this piece of that history in my archives. It seems like there is one anomaly in the data set with the one preamp tube showing a low voltage that doesn't fit in with the trend of things otherwise... no explanation for that.


I believe that this was a Heyboer HTS-5199 Power transformer and not the HTS-9144. You could expect maybe 12 to 15 volts less on B+1 with the HTS-9144. Sorry I don't have plate and screen voltages. They might be included in Gary's chart I just don't recall.

I'll keep digging...

rj

[dehughes]

Nice. Thanks RJ! That helps a ton! I'll live dangerously and go for 250 per side. We'll see!

[RJ Guitars]

I've found that Heyboer rates there transformers using an unloaded figure... for those that aren't familiar this means that without anything attached to it a 250-0-250 tranny will give you 500 volts where an Edcor, Pacific, or Hammond will give you something a bit higher for the same voltage rating.

The 250-0-250 from Heyboer should be dead on for the "official" Rocket specifications.... as best I can nail them down anyway.

rj

[dartanion]

I think you meant "unloaded" RJ.

The 5199 260V taps are pretty nuts on for a Rocket. That is if your wall voltage is correct.

[RJ Guitars]

I think you meant "unloaded" RJ.

darn... your right! I fixed it!

[dehughes]

Right on...I think I'll be good either way....

Thanks guys for helping me suss this out. I look forward to getting this in the amp and seeing what changes in feel it brings about.

[Andy Le Blanc]

this where your gonna want to look at your Ip Ep charts for the tube type
and compare loads at the chosen B+ for Pout and % 3rd order distortion products

Loading decisions should include the DCR of the opt, you can load as you
usually do with the rated impedance per load or you can choose a opt that is
half the rated impedance and then double the load to arrive at the same point.
This will present a reduced DCR to the tube, which will change the proportions
of the harmonic products from the push pull power side.

its a common trick, and a good time to take a closer look at the design choices.
And demonstrate a graphical solution.

[dehughes]

Thanks Andy. Interesting....a "sweet spot" for the EL84 seems to be 300v for va and vg1, with a 130 ohm shared Rk (which is near perfect with my 62 ohm). The THD is higher, but it's right at 8k impedance for the pair...16k for the quad.

However, I like the 250va and vg1 rating better, I'd be getting less THD and significantly less Pout (11w vs. 17) for the pair.

Maybe I'll adjust my power reductions switch to take me closer to the 250v rating (r.e., add a larger dropping resistor....).

[azatplayer]

I played around with my rocket voltages trying to get closer to AC30 spec.
I ended up at 325V using the 260 Taps, HTS 5199, with a GZ34. BUT i had to zener the primaries down about 10volts. That would make 250 heyboer volts about right with a GZ34.
I reckon your target of mid 320's is perfect.

[paulster]

I ended up at 325V using the 260 Taps, HTS 5199, with a GZ34. BUT i had to zener the primaries down about 10volts. That would make 250 heyboer volts about right with a GZ34.

My AC30 build uses a 280-0-280 from Heyboer and has 323V on the plates with a 50ohm cathode resistor, using a Mullard yellow label (military spec) GZ34.

Clearly there is a bit of leeway on the voltages we're seeing, since mine is a Heyboer also.

My voltage droppers are configured the Vox way rather than the Trainwreck way though, so I don't have a single, long, dropping string.

As I said before I'd have the tranny wound with dual taps if it's going to be a custom wind anyway so you can pick the operating voltage that best suits if you really have a specific target voltage.

[M Fowler]

Dynaman had some lay down trannies maybe he still has some in the voltage you need.