Hiwatt DR201 - Voltages not adding up

[Gaz]

I'm about to embark on building a 200W DR201 with 4 x KT88s. Heyboer can wind trannies to the original specs, but I'm noticing something weird on the schematic at Mhuss' site http://hiwatt.org/Schematics/DR_200wPS.gif

The voltages before the rectifier and after just aren't computing. For example, the screen supply is 280VAC and 410VDC after the choke! Even with the unloaded 1.414 AC to DC conversion, you'd still only get 392VDC, and I'm used to seeing 1.35 loaded at most, which would be 378VDC.

Same goes for the plate winding, which is stacked on the screen winding. 450AC, and 650VDC after the rectifier! x1.4 would be only 630VDC and x1.35 would be 607VDC.

I suppose I'l get closer to my calculated voltages, and don't think I'm going to defy the laws of physics with the Heyboer trannies, which are spec'd at 280VAC and 170VAC respectively on the HV windings. However, I'm really curious about the values on the schem and how they came to be.

I've found a few people saying the voltages on their originals were closer to the 650VDC figure, but maybe the primary was rated for 117???

[selloutrr]

Original Hiwatt voltage selector is 105-115-225-245

Worth a look
http://www.chambonino.com/work/hiwatt/hw4.html

http://hiwatt.org/tech2.html

[diagrammatiks]

holy cow that transformer in the link...

[Gaz]

Yeah, I love that site. I like how he's all 'so I just had to rewind it'. Cause you know, that's what we all do right? Just rewind transformers when they die

[bb5000]

I've started the 6xEL34 version of the DR201 and ordered my transformers from TubeAmpDoctor in Germany (more convenient since I'm in EU). Here are the PT specs:

Primary:
0V Black
105V Blue
115V Green
225V Yellow
245V Red

Screen: White

Secondary:
0V Green
220V Black

0V Grey
300V Red

3,15V Black
0V Green
3,15V Black

0V Yellow
40V Red

[Gaz]

Thanks for the specs, but the HV taps look really strange to me. On the schematic they are 280-0 and 170-0 VAC. With you numbers the plate voltage would be around 700VDC!

[bb5000]

Here's a reference also:

http://dst-engineering.com/TN.php?n=HiwattCustom200

[Gaz]

Thanks for the link! I'm still perplexed though because the PT in the in the link is the same one on Mhuss' site, and his measured voltages are even higher! Is this a magic transformer or what? I definitely do not want 730 volts on the plates!!!

[bb5000]

Also note that the primary impedance of the OT is 2.6K for 6xEL34's. That should prevent the tubes from running too hot. The TubeAmpDoctor OT that I ordered is 2.4K.

I've been using the 220V tap with my Weber AB200, 6xKT88's..the average wall voltage here in Sweden is 230V but varies between 220-235V. The plate voltage is 660V, screen voltage 600. The amp has worked ~300 hrs without problems.

[diagrammatiks]

Thanks for the link! I'm still perplexed though because the PT in the in the link is the same one on Mhuss' site, and his measured voltages are even higher! Is this a magic transformer or what? I definitely do not want 730 volts on the plates!!!

you'll get less under load. but even then what's it matter. el34s can take up to 800vdc as long as the screens are kept below 400.

[Gaz]

Yeah, I know it'll probably be fine, but when the whole Internets is telling you all new tubes are shit and can't live up to spec, one can get a little paranoid. When I get the amp done I'll post all the voltages.