lamination orientation

[johnsonad]

Paul,

When you originally designed the Paramount with the top mounted OT and the power supply (PS) choke where the present OT is, what lamination orientation did you plan?  I’m assuming 90 degrees (or opposite) from the PS choke underneath with the bell end facing the tubes?  I ask because Mike is building me a pair of Jr’s and the plan is to top mount them.  I’m debating between leaving the PS choke where it is now above the FS choke or mounting it under the top mounted OT and the orientation of both pieces of iron.   

Regards,

Aaron

 

[jrebman]

Aaron,

HTH,

Jim

Yes, you've got it right for the tfa-2004 jr lamination orientation -- the endbells should be facing the tube and input jack/binding posts, and Paul already told me that it was fine to mount the plate choke underneath, but if using the bcp-15 the holes ill not line up with either of the two sets that are already in the plate, so you may need to mount the choke on some standoffs or some such thing to get enough clearance for fasteners and wiing.  And you'll also need to drill a hole for the wiring from the top mounted tranny.

 

[johnsonad]

Hi Jim, fancy meeting you here

My initial thought was to leave the plate choke where it is and move the Triad power supply choke (PS) beneath the OT where it has close solder pads on the PS board.

Aaron

 

[Paul Joppa]

Jim has it right.

Here's the long story, backwards: I grew up with slide rules, which are logarithmically based. I had a career in acoustics, where frequencies and levels are most often on log scales. For these reasons, I am pretty good at approximate arithmetic (I'm terrible at precision work though!). In the early days of VALVE, Dan dubbed me "Brainiac" for this reason - the old archives have several articles under that moniker. At some point, we developed a design that was a step up from the ParaBee, using a plate choke that matched the TFA-2004 physically; Mike called it the BPC for Brainiac Plate Choke. We made all of two amps that way before other priorities intervened; we no longer have possession of either one. They had the BPC and TFA-2004Ni topside, with the power transformer (PGP8.1) between. The next step would have been to add DC heaters, filament chokes, and PSU chokes, with the filament and PSU chokes under the audio iron. That never happened, and when we went to the Paramount both audio devices had solder terminals (much less costly that end bells and flying leads!) and had to go under the plate. So the chassis got enough deeper to put the filament choke behind the power transformer.

Notice that in all these iterations, the iron is mounted with mutually perpendicular coil axes, and symmetrically placed. I did several experiments to confirm that this really would minimize the coupling - theory takes you a long way, but not all the way. In the ParaBee, the plate choke was in front of the power transformer and under the chassis; it did pick up a trace of hum but the AC filaments made enough more hum that this was not important.

An imaginative experimenter could come up with a huge number of other variant possibilities, if you assume you can get some of the iron in forms that are safe to put topside. :^)

 

[johnsonad]

Hmm, so you're saying Paul to move the plate choke to the other side under the OT or were you referring to the orientation of the top mounted Jr?

Jim, I guess I'm confused as to the size of the BPC-15, I was under the assumption that it was the same size at the BH-7... Looking at the underside there is little room for a bigger plate choke in the present position.  Is it larger or smaller than the standard choke? 

Sounds like if I follow the rule of perpendicular iron it should put me in the ball park either way. 

 

[jrebman]

Aaron,

Sorry, but I don't know the actual sizes yet as I'm still waiting for my mq order.  I also believe it is more the orientation of the coils and not as much the lams, but I could be wrong on this.

With the psu choke under the Jr. the coil axes will be perpendicular still, but what I don't know is if the field strength of the 60 hz on the ps choke is fairly confined to the core, or if it is strong enough to bleed into the Jr.

This is all really in the realm of eucated guesses right now for me as I don't have the iron and have yet to delve into the guts of the paramounts.

I did see some mention of a power supply pc board, and I don't think my amps have those, but I'll check next time I'm in my office.

-- Jim

 

[jrebman]

Ok, before anybody panics -- yes, I do have a psu pc board in these amps.

I ordered a manual from Eillen yesterday, but in the mean time, can anybody tell me what the value of the power resistor on the psu board is, and also what the to-220 devices are?  Assuming they are rectifiers, but not sure if these have been upgraded or not.

-- Jim

 

[Paully]

http://www.bottlehead.com/smf/index.php/topic,1760.0.html

In this thread is a picture of the BCP-15 mounted on the underside of the Paramounts.  I didn't have to drill any holes for it.  There should be holes already offset that it will fit into.  Hopefully this helps.

 

[Grainger49]

Jim,

The Paramount PS resistor is 270 ohms.  I think the TO 220 devices are 600V Cree diodes.  That is, if we are talking about the Paramount power supply board.

 

[johnsonad]

http://www.bottlehead.com/smf/index.php/topic,1760.0.html

In this thread is a picture of the BCP-15 mounted on the underside of the Paramounts.  I didn't have to drill any holes for it.  There should be holes already offset that it will fit into.  Hopefully this helps.

Thanks Paully!