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Old 16th July 2009, 07:48 AM   #1
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Default help on a SE 4 channel tube amp for auto?

Hello all,

I am new here and seeking advice on an amplifier project I would like to build.

Since I am new here just a little about myself, I am a semi-retired television technician (thanks circuit city) who has been interested in and collected tubes and related equipment for years. I recently however decided to build my own first set of amps. I chose a pair of techmaster tm-15a s mainly because I was able to aquire the pair to one I had at the time and I did not consider them as worthy as some of the other units that are waiting for rebuild. The amps were built for my wife for our 12th year, so there was a lot of love built into them. They were built from the ground up, refinishing chasis transformers etc. These are 2 X 6SN7 2 X 6L6 and your favorite flavor of rectifier (5AR4/GZ34 for me in these). They are virtually the same as the heathkit W-2, but they are on one chasis as a W4. They are equipped with the venerable altec 16283 OPTs 7 strand milspec silver over copper and some fabulous Western Electric coupling caps. These amps will now totally blow away my citation II that was rebuilt by GSI (now known as the dual 60 by GSI... late 80s early 90s any info on this rare unit would be greatly appreciated) I also believe that if you are going to take the time to do something you had better do it right. ( one reason why I have collected for so long and have not put my hobby to practice 10yrs, I have yet to feel comfortable altering something that has stood the test of time so long). I really prefer tubes and dislike solid state in the audio application in any form, and last but not least one of my main guiding priciples is KISS (keep it simple stupid), so to me the most elegant solution, is the one that keeps thing simple. Enough about me and what I think, lets get on with the project.....


I would like to build a single ended four channel amp for application in the auto. What I already have for the rebuild (oops I mean build) are two things, the first is a set of coils for the B+ they are merit p-4051 12vdc vibrator in and 265vdc out at 55 ma. These must have some solid state rectification built into the can. I would most likely want to remove this and use an ez80 ez81 6ca4 etc. to do the rectification, however I do not know where the tubes like to operate. (I do not have the design expertise that many of you seem to have in abundance) By using a rectifier I know that we will lose some addl. voltage, and may end up close to 250v.

The second thing that we have to work with are the OPTs which will be recycled from a couple of webcor reels originally designed to run the ECL86 / 6GW8 tubes. I do not know if this idea will work with just the preamp and driver sections of the ECL86 or not. If I am going to need to add a preamp tube to each channels' mix, I may just go with EL84 / 6BQ5 as I have close to 100 instead of say 10 of the ECL86. I am trying to do this with the fewest number of new parts. (I will not build a new circuit with old sockets and the like, but I probably have everything else save a chasis)

I have seen the schemos on this site for a similar application, however with my limited experience I do not feel comfortable making mods... What I need is a circuit minus the tone control that has a (gain control?) (volume control?). I have not been able to locate a copy of the original schemo as a starting off point. I would trace it out and draw it myself, however at that point it would not be of help (you should see the one for the techmaster).
I thank you in advance for your time and help

P.S. The irony that this circuit will derive all of it's power from a solid state source is not lost on me... another hypocritical thing is that I would employ any kind of circuit topology to condition the ac power before it ever got into my amps.

regards Ian
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Old 16th July 2009, 03:26 PM   #2
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If i were to make a valve amp for the car...

i would buy one of those cheapo inverters,--say a 300W one, and rip it apart, and take the 360V DC outta that for the HT. Heaters are fairly simple at 12V....

Then I would make up a 'standard P-P design with the 'usual suspects' so as you have say 20-50W to play with instead of around 5W from an ECL86

nice and simple, although you would prolly have to add extra filtering to the HT supply from the inverter as these operate at a fairly high frequency,--which we dont want getting into the supply rails...
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Old 16th July 2009, 04:33 PM   #3
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Default thanks for your response alastair e

Thank you for your response,

I thought of an option like this, and the obvious easier route of using an existing tube amp and simply using the inverter to power it. What drives the desire for this amp is the parts on hand already discussed and the fact that I have a pisspoor quality se el84 reciever by teeco (cheap cheap) that has just the sweetest sound, not as good as my tm's, but the circuit inside the teeco is 50+ with no mods. Also the low power will mean that all other aspects of the system need to be optimal, thus insuring some additional tweaking to keep me from building something else to soon. (especially important since I am still out of work and parts can be quite expensive.) This keeps the missus happy, plus it will be for her auto.

I sincerely appreciate your time and look forward to seeing you around the board on future discussions

thank you
Ian
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Old 16th July 2009, 04:35 PM   #4
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Perhaps this can help you .......................


http://www.decware.com/newsite/zkit2.htm

Click the image to open in full size.




http://www.tubedepot.com/kitshifi.html

Click the image to open in full size.




http://www.hagtech.com/cymbal.html

Click the image to open in full size.





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Old 16th July 2009, 05:10 PM   #5
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Hmm, Now I see where you're coming from--Been there myself, with no spare cash to 'Waste' on projects!

At the moment, you have the basics to produce what you're after, although you may find its a little low on power output for an Auto application.

The 'Vibrators' that you have, sound like the 'Synchronous' type.--ie, there are two sets of contacts in there. One for the 12V supply and Primary of the Tx, the Other for the HT side, to 'Rectify' the Tx output from the secondary.

The HT sets of contacts are arranged to change-over with each half-cycle at the same time the 'LT' or 12V contacts are, at the exact same time, --In 'Synchronism'--hence synchronous Vibrator....

Best use a standard silicon type rectifier or valve rec, and not bother with the HT contacts of the vibrator as they were rather unreliable--even when new, and were rather 'noisy' (HT borne noise, not so much mechanical noise...)
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Old 16th July 2009, 06:46 PM   #6
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thank you for your replies,

thanks juliovideo the circuit looks simple, and looks like it could be adapted easily to use the 6gw8 as it only uses one side of the triode. since it is already in a kit form if I had the money it might be tempting to go with the pcb's instead of point to point. Of interest to me is the primary of the opt at 10k the transformers I have figured out to about 10k using an 8 ohm out basis, but some of the others I have seen for this app are around 7.5k

hello again allastair we learn all the time here don't we? I had no idea that they had made vibrators with rectification, however it makes complete sense so that they could use a standard coil. (have not ever worked with this technology) The coils or transformers I have are merit and they put out a rectified 265v 55ma they are to be fed an input from the vibrator, this is obviously how they intend to make oscillation to induce voltage over the coil. I am a little worried about the power into the tubes, ie their favorite opperating area, but was well expecting to be a low output power set, with some reasonably effecient speakers there should be enough sound pressure to drive you away from the auto.

thank you again
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