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mikeski's amp

mikeski

mikeski

I need input
So, it has been decided. Thanks to Kegger for the design and interesting tube choices. I am going to build the amp from this link, post #7-> http://www.audiokarma.org/forums/showthread.php?t=321036 and will post an updated version of it when mine is working properly.

I have the A300 Iron
Tubes will be....
a 5V4G for the PS. They come in bottle form.

a pair of 6BL8 for the "direct coupled gain to splitter tube". This tube was designed to be used as a frequency changer in TV receivers.

a quad of 6JB5's. These look like R2D2. This tube was designed to be a vertical deflection Amp in a TV.

I believe I am looking at 20wpc. And it's a clean slate. I have no chassis to start with.

I should probably buy two set's of all the parts. The first to use as a mule. The second for the build of the pretty one.
 
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Always complications. I am told I will need a dual 5V4G setup to get the juice I will need. So I am off to find one already designed so I can plagiarizer it.
 
A single 5AR4 is fine, or depending on what power tranny you have/get
damper diodes are Very Very cheap tubes that are an extremely strong
tube rectifier, if your building from the ground up an DIY'ing use dampers.

6AX4(and many subs/rollers) are an octal version, there are compactron
based dampers as well if you want to use sockets like those outputs use.
 
Looking this over it should scale up pretty well.

Use a 330v B+ power supply, good for 200ma+. (drawing roughly 215ma total)

Roughly 322v(after output tranny drop) at the plate of the output tubes an 315v
at the screens plus this is the splitter supply, 100v at the plate of the 6BL8 input
tube(triode strapped pentode section).

I believe the RC stages should be really close to proper voltages with that scaled
up power supply or very minimal tweaking, looks like 270ohm cathode resistors for
each pair of 6JB5, and probably bypass cap on the 390ohm input cathode resistor
for some extra gain for the 6JB5, needing a bit more drive then an 6K6, 6V6, EL84.
 
This thread shows a parallel 5V4/5AR4(same pin-out) Post #22
http://www.audiokarma.org/forums/showthread.php?t=309374&page=2

There are 2 ways to parallel them, each rectifier powers that whole supply using
1 plate per ac input, or parallel each section of each rectifier then 1 rectifier one
side of the ac coming from the power tranny and 1 does the second half of it.
(not sure which way I prefer, if someone does please post about it here) :)
 
Schweet. Just what I was looking for. I may have found it eventually. There is so much out here. Search has it's issues. I have my issues.

Really. I am not a pro at this. I learned all about Radio and TV repair in Boces in NY back in 75 - 77. That's my main exposure to tubes. Repaired cards from radar on A6's and then did test equipment repair and calibration in the Navy. Some calibration and repair after the navy, office equipment, computers. I did manage to rebuild my PAS3 and ST70 recently. But that was all kit stuff. I can fix my TR6 electrical. I forgot most of all that stuff. Just the basics are left in the head.
 
With that background you should do well I'd think.. :)

Do you have a power tranny yet?

Do you have any power supply chokes, and or did you want to get some or go cheap an use resistors?
 
I have the power and output transformers from an A300. Well, they are in the mail. So I am starting from scratch. Not even a chassis. I will use a metal plate for the bed and then set that on a wood ring.

I do not wish to go cheap on the parts. I will buy parts over the next few months. That's actually what I am trying to do. Finalize the design so I can put my parts list together.

The PS schematic helps. Instant parts list.

I will start with the other schematic for the 6k6 output in the pointer at the top of this thread.

I started rooting around in the forum also for favorite/preferred suppliers. Gota know where to go to get the stuff.

My audit group is suppose to be going to Tokyo again soon. I will need to see if i can get on that one. I would love to take the parts list with me there.
 
So you plan on using the power tranny from the A300?

If so it will be totally different then anything we've been talking about.

The HK used voltage doublar and SS rectification, not saying you can't
use it, just it will not be what you've been envisioning for this build here.

----------

The heater winding on that tranny would be stressed a bit as well using
the 6JB5 output tubes, myself I'd look for another PT..
 
Oh well, I like what we have been talking about. I can shelve the A300 iron for now and build a 300 clone with that. Or use the 300 outputs and just find a power transformer that will fit the bill for this amp thought.

hahaha, can't be simple.
 
Damn, I'm going to need a big transformer.

4 6JB5's at .8a = 3.2a
2 6BL8's at .45 = .9

2 5V4's at 2A = 4a

Then we talked about needing 330v of B+. About 250ma I think.

So....
5a on the 6.3v.
4a on the 5v.
250ma+ on the High voltage AC. The 370v shown in the dual 5v4 PS should be good.

Is that 370v across the output or 185v from the tap to the end? or 370 from the tap to each end?

Damn, it almost sounded like I knew what I'm talking about.
 
Yep the output transformers are fine. (but the power tranny just doesn't cut it) :(
(even doing EL84's would be stressing that PT, not as much as the 6JB5's would)

If you come across some power tranny choices or thinking of something just shout.

But yah if doing 1 power tranny for a stereo amp you'll need/want something in the
285-350v range(you can make that work with different caps/chokes/resistors) and
225-300ma range, then all your heaters voltage an current of course.
(when I say 300v tranny yah it's 300-0-300 or 600v ct)

The one in the linked schem would "work", you'd be drawing an bit less current then
that amp so you'd need more resistance in the supply to bring the voltage on down.
(but that is certainly a beefy tranny that would work here though)

http://www.triodeelectronics.com/mq060.html

---------

If going Damper Diodes for rectification these two would be something like your after.
( otherwise you'll need that 5v winding to, there is also a 6BY5, 6v version 5V4 :) )

http://www.edcorusa.com/products/615-xpwr023_120.aspx

http://www.edcorusa.com/products/739-xpwr137_120.aspx
 
Just an example using that large st70 replacement tranny something like this
would get you the "proper" voltages. (think of the 5ar4 as parallel 5v4/6by5).
(you could also eliminate 1 choke section and use a single 150ohm instead)

-You can play around with that PSUDII to see what kind of options you have.
 

Attachments

  • 6JB5_6BL8_330V_SCH_PS.GIF
    6JB5_6BL8_330V_SCH_PS.GIF
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Kegger said:
This thread shows a parallel 5V4/5AR4(same pin-out) Post #22
http://www.audiokarma.org/forums/showthread.php?t=309374&page=2

There are 2 ways to parallel them, each rectifier powers that whole supply using
1 plate per ac input, or parallel each section of each rectifier then 1 rectifier one
side of the ac coming from the power tranny and 1 does the second half of it.
(not sure which way I prefer, if someone does please post about it here) :)
Click to expand...

If you're wiring from scratch, it's probably better to parallel both plates in a rectifier tube, and use one whole tube for each end-tap of the primary. That way, if one dies or is removed, the other one won't get "overloaded" as much (you'll lose one "phase"... the B+ will drop... but it won't try to draw obscene amounts of current from the one remaining rectifier).

Regards,
Gordon.
 
That's how I have both my amps I've built with parallel rectifiers wired, an for the same thought process. ;)
 
I'm not dieing to use the 5V4. Just interesting to be different. And this would be parallel 5AR4.

I have an ST70 and thought about checking into that trannie. overkill is ok ;-).
 
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