Eimac 35TG amplifier glows !

[ReinoutdV]

Good evening all,

at last....just finished my Eimac 35TG amplifiers. This took simply too long....but was worth the waiting !

After a great start i had troubles with the first stage (6HV5A) and decided to switch for another compactron (6FJ7). The 35TG stayed; great tube. There are not many amplifiers with this triode out there. The amplifier is set up to accomodate the 100TH also (but i have stacked enough pairs 35TG's to last for some time....).

In the next pictures i'll show the work in progress ending with the finished product.

The first pictures are about the designing and drawing. You see that i am rather old-fashioned: everything on paper (no computers). I simply want to see the design on a 1:1 scale !

Happy reading !
Greatings from the Netherlands,
Reinout

[ReinoutdV]

The next set of pictures are about the components.

All the transformers were ordered (no standard of the shelf products). But....that gave me the opportunity to ask funny items like stacking a coreless coil on top of a choke (a standard way of building i always practice).

Metalwork is arriving:
- extruded profile for the sidebars;
- stainless steel top- and botomplates;

Reinout

[ReinoutdV]

This set contains pictures of the building start and breadboarding.

The rectifiers (all IXYS hexfred's) are mounted on a red copper slab. This transfers the heat to the metal casing itself. There is no need for extra cooling fins.
The rectifiers for the B+ is a 2000 volt affair. More than enough for the 800V for the 35TG plate-voltage.

The amplifier started of with a compactron (6HV5A) as first stage. This was not stable. It worked....but did not sound the way i wanted. With another compactron (6FJ7) a new first stage/driver was made.

Reinout

[ReinoutdV]

More pictures of the building phase.

In the end i needed some serious resistors to reach a stable voltage for the 6FJ7. Caddock-resistors are great to use: they are really milspec and up to their task.

First i was planning to have the 6HV5A also in parafeed. But now the 6FJ7 is in a Lofton-White configuration (the 35TG is still in parafeed). The left-overs from the first stage (6HV5A) were simply too good to let them on the shelf. So now the first capacitor in the B+ voltage rail is a Mundorf Silver/Oil 2,2 uF / 1200 VDC . Somewhat over-rated....but shockingly stable !

Reinout

[ReinoutdV]

The amplifiers are working:
- great bass-respons (and NOT sloppy);
- good definition;
- clean but not too analytical.

All in all a very nice musical result.

The 35TG looks small but gives a serious output. At the current 800 VDC i get serious 10 Watt of of it.

Reinout

[Jeffrey Davison]

Very very nice... I'm in process of a 304TL myself.
May I ask who made your transformers?

Thanks!

Jeff Davison

[ReinoutdV]

Details:

This 35TG has cooling fins. The 35TG is made for quite some time......i have therefore quite some versions of this triode.

The anode is made of tantalum. Later it was made of molybdene with zirconium coating. I like the tekst "the tantalum plate is designed to run hot. Only a perceptible glow can be seen at 2 Watts dissipation, and a dull cherry red colour at 50 Watts dissipation. This is normal, and no damage will result at this temperature. The convenience of the use of the plate colour as an indication of proper circuit efficiency and tuning will be appreciated after trying"............

Problems with these thoriated tungsten filaments: they become brittle after use. So the last years i am collecting my stash of 35TG's. More than halve of them were broken......but trust me: i have enough pairs to last for a serious amount of musical delight.

Regards,
Reinout

[TheGimp]

Sweet!

[ikoflexer]

That is very nice. I dream of building something like this with my spare 1200V transformer. It'll be a long time before I attempt anything of this magnitude though. Nice work, thanks for sharing!

[ReinoutdV]

Good evening all,
thanks for the positive comment. I am very happy with this amplifier. It is a scaled down model from the BIG amplifier (on the background at one of the pictures visible). The big ones are simply non-movable (300 kgs +).
The schematic, component-choise, etc is in essence the same.....just smaller...

These 35TG's "only" weigh 50 kgs each....so managable. If there is another audio-gathering i can take these with me.

To Jeff: all the transformers were made by Stoet. This is a firm in the Netherlands. With regret i must report that these fine transformers are not available anymore (manufacturing stopped). This was my last project with all-Stoet transformers.
For my new projects i have already very nice results with Silvercore (from Germany) and AE (from the Netherlands). Of course i look for transformersuppliers on this side of the ocean....that will spare me serious postage-costs.

Regards,
Reinout