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6C33C cathode follower, slimline power amp (design: Suncalc)
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Author:  mwhouston [ 24 Aug 2017, 07:45 ]
Post subject:  6C33C cathode follower, slimline power amp (design: Suncalc)

Once more I put it on Suncalc to design me a 6C33C cathode follower amp. The whole crux of this project is to have these large tubes jutting out of a 1U 19" rack mount enclosure. And only the tubes exposed. No OPTs or trannies of any kind. I had seen a commercial version of this idea which used SMPSs and wanted to copy the idea.

What I will have to do is power the amp with an external tranni box. Because I require 6A at 12V to power the 6C33C heaters and 300VHT at just less than 400mA the trannies must be robust. Two 160VAC trannies, back to back should do the job. The 12V tranni is rated at 12A.

The design uses a 4S driver stage and will allow driver stage tube rolling. I have a quite few different 12A*7s. The big bonus with the external tranni box, with XLR sockets, is I can us it to power lots of other amps. This is a similar idea to the 6L6 tranni box I recently made. This time though the box will rectify and two stage filter the HT. That means in the ampamps I only need limiting resistors and a final filter stage. Save lots of money and allows easy amp rolling.

I have started on the tranni box, images to follow. Take a llok at Suncalcs design;-
Attachment:
6C33CSchematic.jpg

Author:  M. Gregg [ 26 Aug 2017, 07:38 ]
Post subject:  Re: 6C33C cathode follower, slimline power amp (design: Sunc

Its interesting to see the ideas,

Also not many comments :)

These tubes 6c33c are like cooker elements (very hot).
The biggest problem is usually the driver stage and blocking distortion usually overcome with higher voltages on the driver stage.
When I used the 6c33c in an OTL I burned the tubes in for 12 hours (heaters only) before applying HT.
This is based on many peoples comments about tube failure if they aren't burnt in. (something to do with the elements expanding into position) but each to their own ideas.
I used them in mixed bias.
On an OTL it is possible to use heater selection I used Left/ right /both so I could reduce the power consumption with single heater.
The left / right meant I could get equal wear over a period. Interestingly the tubes change sound after a while running, this was obvious when changing from one side heater to the other on first run. (burn in).

For interest I used my heaters in series to cut the current which seemed to fry the sockets when in parallel.
I floated the heaters with a capacitor.
That's just my thoughts. I'm sure there are many builders that have more extensive experience with 6c33c than I do.
Romy the cat has/had a site linked to these type of tubes.
http://www.goodsoundclub.com/Forums/Sho ... ostID=6140
Best of luck..

Regards
M. Gregg

Author:  M. Gregg [ 26 Aug 2017, 08:05 ]
Post subject:  Re: 6C33C cathode follower, slimline power amp (design: Sunc

Thought it worth a mention,

I run 4 6c33c and the listening room heats up very quickly.
It sounds good but again is coupling cap dependant<< I melted Jupiter wax caps and oil caps in the chassis nowhere near the power tubes behind a heat shield.
I eventually sorted the heat flow.

Regards
M. Gregg

Author:  mwhouston [ 26 Aug 2017, 10:03 ]
Post subject:  Re: 6C33C cathode follower, slimline power amp (design: Sunc

I though each tube required 6V for the hearts in total. I have 12V @12A tranni. To me I can run the two tube heaters in series. Right.

Author:  mwhouston [ 26 Aug 2017, 10:07 ]
Post subject:  Re: 6C33C cathode follower, slimline power amp (design: Sunc

It's alright I have it sorted.

Author:  M. Gregg [ 26 Aug 2017, 11:58 ]
Post subject:  Re: 6C33C cathode follower, slimline power amp (design: Sunc

mwhouston wrote:
I though each tube required 6V for the hearts in total. I have 12V @12A tranni. To me I can run the two tube heaters in series. Right.


The more voltage you can use the lower the current (as you know :) )
So its better to run in series I used 24V but that was for 4 tubes.
I also switched the heaters, however I guess you are just using both sides of the tube.

I run the driver with DC heater and 6c33c AC.
I found a few problems trying to balance the hum but that's a different story.
You need high melt point solder on the bases. I used different solder on the heater connections.

Cathode bias creates heat, lots of it.
The tubes seem to sound different depending on bias type.
However I just thought it might be some use.
Things like flying leads and remote power supplies suffer with volt drop over distance linked to current draw by the equipment.

In these kind of builds think CURRENT<<its a main priority also PSU is or can be dangerous.
I switched off while testing during the build and dropped a B+ wire on the chassis it hadn't discharged completely, it blew a 1mm hole straight through a 3mm piece of aluminium. Be careful.. :up: That was on an OTL your amp may be different.
The capacitors can supply high current with 300v the mA rating of the tube draw is misleading.
I'll shut up now. :D

Regards
M. Gregg

Author:  M. Gregg [ 26 Aug 2017, 12:37 ]
Post subject:  Re: 6C33C cathode follower, slimline power amp (design: Sunc

One other thing I found with OTL,

The more current you can deliver the more bass drive you get. And transient response!
Ie chokes reduce bass, however I wound a couple and used them in the PSU.

Even cable type and cross section made a difference, so its something to consider with types of leads/ plugs and sockets.
Sorry I'm getting side tracked. :sleep:

Regards
M. Gregg

Author:  mwhouston [ 26 Aug 2017, 18:00 ]
Post subject:  Re: 6C33C cathode follower, slimline power amp (design: Sunc

All good info. Thanks.

Author:  mtlsir [ 05 Jan 2018, 22:06 ]
Post subject:  Re: 6C33C cathode follower, slimline power amp (design: Sunc

Hi mwhouston, did you have proceded with this amplifier, i am rather curious. It seem rather simple operation, it would be a good match with high effeciency speaker.

Author:  mwhouston [ 06 Jan 2018, 02:32 ]
Post subject:  Re: 6C33C cathode follower, slimline power amp (design: Sunc

mtlsir wrote:
Hi mwhouston, did you have proceded with this amplifier, i am rather curious. It seem rather simple operation, it would be a good match with high effeciency speaker.

The PS design I was going to use didn't work and left me wondering how I was to get the voltage and the huge filament current required. I have come up with another way to do it, a voltage doubler. In the meantime I got a couple of commission jobs and was distracted by other projects.

Not off the todo list just must finish a couple of jobs I started including a Jean Hiraga le monster.

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