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Voice of Music model 1450 mono tube amp


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Mr. Medwin, 

Your suggestions are appreciated. I am by no means an expert at this kind of thing but my soldering skills are ok.

These 2 amps are in very good condition so your recommendation is understood. My CD player does not have a volume control. I was planning on procuring a tube preamp with no tone controls so I would ultimately get stereo sound instead of mono and use the amps tone controls.

i may reach out to you in the future regarding this project. I assume Mr. Percy is a member of this forum?

Thanks.

 

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You can connect the CD player directly to the phono input.  The amps should be fully recapped (in particular, all the electrolytic and coupling caps).  All resistors should be checked for tolerance and replaced as needed.  The power cord should be replaced with a 3 wire type and the primary of the power transformer needs to be fused.  Otherwise, I don’t agree with Jeffrey’s recommendations.  These are fine amps in their stock form and, while far from being the ultimate, can provide a pleasing experience.  I say this as someone who is not particularly fond of the EL84 tube.

 

 

Maynard

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Jeffrey,  I like tone control circuitry as it allows the user to tailor the sound to their personal taste. And, the 1 meg input load will make the CD player very happy.  Your second thread,  in which you advocate a significant circuit change, was not there earlier.  It could work.  However, eliminating the nfb loop will likely make the amp sound like crap unless running at a fraction of its output power capability.   There really is nothing wrong with this amp as originally designed.  If anything, a different output transformer would probably yield the greatest improvement, but I don’t advocate doing that either.  
 

One last point, it wouldn’t hurt to put a bleeder resistor of around 240k across the power supply filter network as a safety feature.  
 

 

Maynard

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On 5/31/2020 at 2:50 PM, Could sound better said:

I have 2 of these mono tube amps that I would like to recap and incorporate into a 2 channel system. 

My question is: these amps only have a phono input. Do I need to alter the wiring to make them play thru a CD player?

thanks.

 

It looks like it just has standard, rather basic, bass and treble controls; it doesn't look as if it has RIAA compensation (which is good, because you don't need or want that, when driving from a CD player).  So the best thing would be just to try it as is, after following Maynard's suggestions about recapping and adding a 3-wire mains cable. One amp takes its input from the left-channel output of the CD player, and the other takes the right-channel output. 

 

Tone controls are like a red rag to a bull in some "audiophile" circles, but they have their uses and plenty of people like to have them.  These amps are never going to be super hi fi, so the best thing is just to try them out, after the basic safety replacements a la Maynard, and see what you think of them.

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Jeffrey, you are far too concerned with the gain of the input stage.  Amps like this were typically used with ceramic or crystal phono cartridges having an output of as much as a few volts.  The feedback network employed reduces the gain to a specified degree.  Also, the 1meg input load was usually sufficient to allow the cartridges to function with their own “RIAA equalization.”   Why are you trying to redesign this entire amp?  Given that the EL84 DC plate current draw won’t vary by more than a couple of milliamps or so between idle and full output, having a 1K filter resistor is of no consequence.   While this amp may not meet your standards, it certainly can provide a very enjoyable listening experience  for most  when using Klipsch speakers.

 

 

Maynard

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10 hours ago, Jeffrey D. Medwin said:

When replacing the QUAD CAN with a new one, I would suggest making the FIRST section only 20 uF  ( as seen by the rectifier tube ) , and not 40 uF. as shown stock. 

 

Wire it as  :  6X4 /  20 uF  / 1000 Ohms /  40 uf   - to FINALS   /  etc.  etc, ..................and not vice versa uF amount wise.

 

I don't think filtering will be substantially effected, either way, .......  but it should be somewhat easier, more conservative, on the 6X4 rectifier tube.

 

Maynard, or Backfire, what do you gentlemen think??

 

Jeff 

 

 


What you propose is reasonable!  
 

 

Maynard

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13 hours ago, Jeffrey D. Medwin said:

When replacing the QUAD CAN with a new one, I would suggest making the FIRST section only 20 uF  ( as seen by the rectifier tube ) , and not 40 uF. as shown stock. 

 

Wire it as  :  6X4 /  20 uF  / 1000 Ohms /  40 uf   - to FINALS   /  etc.  etc, ..................and not vice versa uF amount wise.

 

I don't think filtering will be substantially effected, either way, .......  but it should be somewhat easier, more conservative, on the 6X4 rectifier tube.

 

Maynard, or Backfire, what do you gentlemen think??

 

Jeff 

 

 

Yes, 40uF would seem to be pushing the limits of what is recommended for a 6X4, so certainly switching the 40uF and the 20uF around so that the 20uF is the one coming directly after the rectifier would give a bit of extra margin.

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