All this talk of RH-84 amps inspired me ...

[TomMcNally]

I built a three channel version last year ...

sounded really sweet, and
a 6V6 version a while back ...

so over the last couple of days I built
another one from the original schematic.
Sounds great.

I used an Edcor XPWR008, and Edcor GXSE10-16-10K Outputs,
and a Hammond 158M choke. I didn't measure any voltages.
Thanks to Alex for the design.



Disregard the extra holes under the power transformer. Pilot error.
I made the forked tag trips for connection points, pretty handy.

[20to20]

Tom,

There's a fellow on the DIYAudio board looking for a custom builder, if you are interested. He asked for a "skilled" buider. (Won't mention pilot error.)

Hope all's well!

20

[roren]

Beautiful work Tom.
I only wish that I was half as productive as you.

[HeyItsBen]

Second on the beautiful work as always, Tom. I've got a great big big directory full of McNally upskirts that I refer to all the time to show me how nice PTP can look, not that I'll ever achieve your level of workmanship (or productivity, jeez).

I've also caught the rh84 fever that's going around, and made it my first PTP amp project.
Added level of difficulty: somebody else's half-abandoned console-pull chassis, junk drawer parts (new 'lytics, though).

So I'm curious about those 47uF lectros you used instead of the 10uF- will it make any difference? Or, better put, will I hear any difference?

-Ben

[jollyrogr]

Tom you must buy hammond enclosures and edcor transformers by the pallet load...

[TomMcNally]

20to20 .... I looked up that thread. That guy wants an "artistic" type chassis,
that's not my forte ... but thanks

roren .... Thanks - I love to build. Usually goes in two steps, first do the
metalwork and bolt the parts in. Then solder it together. Then
listen to the music !

HeyItsBen .... Good to hear from a newbie on the board. Thanks !
They are lots of skilled builders on our forum, I just
happen to be the fastest, not necessarily the neatest.
I have a box of hundreds of those 47's ... and I don't
think the value in that spot is very critical, it's just to
decouple the low level stages from the outputs.

jollyrogr ... I usually grab 3 or 4 chassis at a time from Angela, and
a couple of sets of Edcor transformers so I have what I
need when the urge strikes.

November seems to be my amp building month anyway, and with the
two major storms that hit New Jersey over the last six months, I didn't
do much over the summer.

... tom

[Alex Kitic]

November seems to be my amp building month anyway, and with the
two major storms that hit New Jersey over the last six months, I didn't
do much over the summer.
... tom

Great amps, Tom! I was particularly impressed with the 3 channel RH84 setup... are you going to try the RH Universal?

BTW, must be great living in NJ... never mind the storms, those happen everywhere...

[johnf]

Just wanted to thank Tom for all the posts and images. I used his P-P builds as a reference point for my RH84.
If I had paid more attention earlier I could have used a 250-0-250 tranny as I have had to drop the B+ with a 150R to get it down to 300v with the Edcor XPWR106-240, EZ81 rectifier and 158Q choke.
I am also running it on a Jan 12AT7WB(1967 vintage) from NOS store in Ankara and Russian 6P14P from sovcom store on Ebay- both very reliable suppliers.

http://s1062.beta.photobucket.com/user/ ... sort=3&o=2

If anyone is interested I found this tape which I put over the transformer laminations. I stole the idea from Leak who always taped their trannys. Not sure if you can get it in the US
(Tesa extra power-matt black on Amazon UK-cheap)

I also resprayed the black Hammond chassis with a darker blue RAL colour to go with the RAL5010 that the Edcors are painted with.
J

[jollyrogr]

Just wanted to thank Tom for all the posts and images. I used his P-P builds as a reference point for my RH84.
If I had paid more attention earlier I could have used a 250-0-250 tranny as I have had to drop the B+ with a 150R to get it down to 300v with the Edcor XPWR106-240, EZ81 rectifier and 158Q choke.
I am also running it on a Jan 12AT7WB(1967 vintage) from NOS store in Ankara and Russian 6P14P from sovcom store on Ebay- both very reliable suppliers.

http://s1062.beta.photobucket.com/user/ ... sort=3&o=2

If anyone is interested I found this tape which I put over the transformer laminations. I stole the idea from Leak who always taped their trannys. Not sure if you can get it in the US
(Tesa extra power-matt black on Amazon UK-cheap)

I also resprayed the black Hammond chassis with a darker blue RAL colour to go with the RAL5010 that the Edcors are painted with.
J

Not sure if my skills using PSUD to model power supplies are up to snuff, but I modeled it quick using your PT, rectifier, choke, and a 47u and 220u cap and came up with around 318V B+. Sound about right? You could try a different rectifier tube with more sag and maybe not need the resistor? Also noticed that PT doesn't have a 5V tap, you must be using the 6.3V tap for the rectifier heater as well?

[DeathRex]

He's using a single EZ81. I think that is the only FW rectifier he can use with the RH. Another I know of the 6BW4, it has alot more drop, but only has a rating of 100ma.

You can see his post here

[johnf]

Thats right. The 6.3v winding feeds all the valves. The amp is really quiet though.
See also a post from "justmikey" in the RH-84 Three Channel Amp thread. He seemed to get B+ of 290v from a very similar configuration. Maybe my PT was over the spec voltage? Though the 6.3v winding was dead on under load.
Anyway I think I can live with the dropping resistor.

[jollyrogr]

Could be the choke. Unless you had the exact same choke that would be my guess. Lots of different impedences in chokes

[justmikey]

Here's the final schematic of my RH-84. I am not the best computer jock, hopefully the schematic has uploaded here ok. The photos I tried to upload just resulted in a "The file is too big, maximum allowed size is 256 KiB." message.

[johnf]

Just wondered about some of the cap and resistor values you changed in the circuit. Any explanation appreciated.

If you want to upload images, save them as JPEGs and you usually get a slider to reduce the file size- well you do on a Mac

[justmikey]

Actually, I built this amp with parts I had on hand. I wanted to use all small nine pin tubes, and I wanted to minimize voltage drop at the rectifier because my PT was only 275-0-275, hence the rectifier choice. The 390uF cap was a snap-in cap left over from a previous project that used PC boards so I used it. Some minor resistor and cap changes were simply because I had them in my parts box. The only really intentional change was the larger resistor from B+ to the EL84 screens. With the original resistor value, the screen voltage was a little higher than the anode voltage, and I felt it would be best if it was the same or slightly lower. The only thing I actually had to buy for this whole affair was the little hammond 6x10 steel chassis and a can of paint. This just shows us what can be done if you never throw away perfectly good extra parts and if you are will to adjust a schematic within reason. This amp sounds great.