Amp Building

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sheepdip
Junior tube assistant
Posts: 1
(3/6/04 12:06 pm)
  AMP BUILDING
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After looking at the avaliable Bass amps out there I have decided to try and build my own. I have an Amateur Radio Extra Lic. and am technically capable of building it but need to know a few answers.

I know that Ampeg built an amp with a RF tube, the 6146W, and am wondering why other RF tubes could not be used. How about some 4-400's or even jump up to the 3-500Z or 4-1000???? Is there something in the output or construction of these tubes other than their size that prevents them from being used in an audio amp?
 
Tiny Daddy
I will work on all amps
Posts: 527
(3/6/04 12:40 pm)
  Re: AMP BUILDING
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Yes ther is something wrong with tubes such as 4-400A: There is no getter other than the plate which must be run hot (say orange) or the tube will become gassy.
Even the 6146 has a problem: it is too short and the heat from the plate causes the base to come loose. The taller 807/6146 is OK for guitar. Also 829B if you can come up with the regulated 200V for the screen.
 
sheepdip
Junior tube assistant
Posts: 2
(3/6/04 12:57 pm)
  RE amp building
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O.K. A regulated screen could be accompolished with a xfmr from Peter Dahl, I see no problem there but I am starting to see other problems. Weight and size are starting to pop up their ugly heads, also cooling these big puppies is going to take some quiet fans. I can see the possibilities of an easy 500W of bass audio driven into some nice JBL's albiet with size and weight sacrifice. Any thoughts on this from the group????? should I just go get a current production tube amp?    
 
Tiny Daddy
I will work on all amps
Posts: 528
(3/6/04 1:12 pm)
  Re: RE amp building
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You may want to check out ceramic-metal tubes such as 4CX250. I don't know how these are gettered but they are good for 35 or 40 watts dissipation with no cooling fan. A disadvantage is, you must keep the cover on the amp because the high voltage is exposed on the plate. Another thing, most output transformers are not good for the 1000 or more volts required to bring those large tubes into linear conduction.


www.svetlana.com/docs/Tec...ll-hf.html

 
sheepdip
Junior tube assistant
Posts: 3
(3/6/04 1:39 pm)
  Re: amp building
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Nope, Not interested in ceramic tubes. they are not the same as glass envelope and the audio will suffer. You are correct abt the HV. One has to be VERY careful around these tubes. Peter Dahl can make a xfmr for anything and his products are the best there are. I am looking at the Eimac "care and feeding of power tetrodes" but there is no audio information  
 
sheepdip
Junior tube assistant
Posts: 4
(3/6/04 2:17 pm)
  Re: amp building
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 "Get Down" There is info out there! You power freaks are going to love this!

If you want to devote some time and MONEY we can be looking at about 3KW of low distortion power using a pair of 4-1000A Tetrodes or 750W from a pair of 4-250A's. You can drive with a pair of 6SJ7's but you'r going to need 2500V on the plates and 350-450 on the drivers  
 
6G6
Junior tube assistant
Posts: 109
(3/6/04 5:44 pm)
  Re: amp building
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  Where's the "shocked shitless" smiley?

OK, I'm impressed  , I bet you can build an amp that big!

One tiny question...do you plan to move it?
I stopped hauling a pair of two 15 cabnets long ago when I figured out that even if they do look mighty impressive, my back just wasn't getting any younger.

Another consideration might be the wiring in your average bar.
If everything goes black when you take it off standby, your gig is already over and you won't be asked back.

Still, I am kinda fasinated.  
 
Tiny Daddy
I will work on all amps
Posts: 529
(3/6/04 6:39 pm)
  Re: amp building
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 I worry what would happen if the speaker chassis connection came loose and let the nasty voltages out onto the speaker leads.
 
sheepdip
Junior tube assistant
Posts: 5
(3/6/04 7:30 pm)
  Re: amp building
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Well, Here is my thoughts on the subject. While I don't like to be discouraged from building these things I am well aware of what the end entails.

First of all this is going to have to be run on 240v. Then lets go into cost. conservative estimate is $700.00 just in tubes. Then there are the custom Peter Dahl xfmrs and chokes probably another grand at least, then the tube sockets, blower assembly, etc. it goes on and on.

With something like this you are going to have to connect the speakers very well. and when you power down do it through large bleeders.

I have a pic of an RF amp that I hd that would do 5KW no problem running four 3-500Z's. The PS was SS and still weighed in at 100lbs.

It could be done but I would have to be a big draw at Madison Sq. Garden and that ain't never going to happen.

I want everybody to at least give me the ATTA-BOY for coming up with the idea.  

Edited by: sheepdip at: 3/6/04 7:34 pm
 
6G6
Junior tube assistant
Posts: 112
(3/7/04 10:00 am)
  Re: amp building
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OK, atta boy!  
I have to admit, I have wondered about 811s and 813s, but then you are getting into uncharted territory as far a audio use is concerned.
It might be more practical to build a pair of SVTs.

Or if that's too conventional for you, do a search for the baga project.
There is something special about using transformers that require a hoist to move them.
 
 
Tiny Daddy
I will work on all amps
Posts: 533
(3/7/04 10:51 am)
  Re: amp building
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For something entirely different check out the 7094 tube:
www.mif.pg.gda.pl/homepag...7/7094.pdf
Would have already tried it but they seem rare and expensive.
 
sheepdip
Posts: 6
(3/7/04 12:01 pm)
  Re: amp building
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 I wonder if I would know the 7094 by a different name. That number sounds like a military number and that tube looks very much like a 4-400 and the specs are almost the same. I'll do a little research.

the 811's would work also but instead of those I would pick the 572 a more rugged interior and easier to get without using the china crap. good thought I didn't think about the 811 series. there are many tubes out there that are used in the amateur radio hobby that would work in audio and these puppies will put out the sound power make no mistake about it but there is a trade off in size and voltage  
 
Tiny Daddy
I will work on all amps
Posts: 534
(3/7/04 1:41 pm)
  Re: amp building
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 7094 has a septar base like the 829B
 
sheepdip
Posts: 7
(3/7/04 4:34 pm)
  Re: amp building
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 Although the 4-400 is getter-less so to speak there is nothing wrong with running them with orange plates. done all the time with older commercial radios that use the tube.

Have you ever seen a 6146 with a loose base???? I have gone thru a lot of those and hve never run across one. I have seen them with the sides caved in about 1/4 inch from miss-tuning heat but still able to put out 100W.

Rather than the 7094 (scarce and expensive) I would explore the Eimac 3-500Z or the Svetlana 572B They both have Graphite getters and think they would make nice audio tubes. One 3-500Z or two of the Svetlana's would deliver audio into the easy 500w range with lots of headroom and not too much size difference from a SVT-CL and probably the same weight or close to it. I think these two tubes deserve some attention from audio amp builders. I think that you know more about audio amps than I do, why don't you look into it a little bit and tell me what you think?  
 
Tiny Daddy
I will work on all amps
Posts: 535
(3/7/04 5:20 pm)
  Re: amp building
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 It's been done, for example:
www.svetlana.com/docs/Tec...No.22.html

And there was an amp, Macintosh or Marantz a few years ago using 300B driving 572B outputs.

The problem with orange plates is not the tubes which are designed to run that way, but rather the DC power required which must be supplied through an audio transformer of large proportions. While modulation transformers with limited frequency response are available it is much more difficult to achieve wideband audio response above 200 watts output.
 
sheepdip
Posts: 8
(3/7/04 8:32 pm)
  Re: amp building
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 O.K. so why not use a 1000v center tap with taps for filaments for the PA tube and the Drivers. regulate the filament voltage with pots (over kill but keeps them going longer) and build a full wave bridge doubler circuit. this will give you the necessary voltages with one input xfmr.

BTW tetrodes are out because of tertode kink but you probably already know that.