Could sound better Posted May 31, 2020 Share Posted May 31, 2020 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. Quote Link to comment Share on other sites More sharing options...
Could sound better Posted June 2, 2020 Author Share Posted June 2, 2020 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. Quote Link to comment Share on other sites More sharing options...
tube fanatic Posted June 2, 2020 Share Posted June 2, 2020 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 Quote Link to comment Share on other sites More sharing options...
tube fanatic Posted June 2, 2020 Share Posted June 2, 2020 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 Quote Link to comment Share on other sites More sharing options...
Could sound better Posted June 2, 2020 Author Share Posted June 2, 2020 Maynard, thanks for the input. If I left the tonal controls could I create a tonal circuit with new caps & resistors following a schematic of the tonal pack like the in the attached photo? Quote Link to comment Share on other sites More sharing options...
Could sound better Posted June 2, 2020 Author Share Posted June 2, 2020 The photo is from another amp I have but the VOM has a similar tonal circuitry Quote Link to comment Share on other sites More sharing options...
tube fanatic Posted June 2, 2020 Share Posted June 2, 2020 Are you saying that the VOM tone control circuit components are contained in a couplate which looks like one in the photo above? My memory is hazy on what VOM used. Maynard Quote Link to comment Share on other sites More sharing options...
Backfire Posted June 4, 2020 Share Posted June 4, 2020 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. Quote Link to comment Share on other sites More sharing options...
tube fanatic Posted June 4, 2020 Share Posted June 4, 2020 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 Quote Link to comment Share on other sites More sharing options...
Could sound better Posted June 4, 2020 Author Share Posted June 4, 2020 Backfire, I have tried them out thru a CD player and a turntable. The sound isn’t too bad, rather nice but veiled. Almost like a a curtain in front of the speakers. Gonna recap, iec, & fuse for now. thanks!! Quote Link to comment Share on other sites More sharing options...
Could sound better Posted June 4, 2020 Author Share Posted June 4, 2020 Thanks to all for contributing to this endeavor. i’ll consider all before I decide on a course to follow. thanks Jeff!! Cheers!! Quote Link to comment Share on other sites More sharing options...
tube fanatic Posted June 7, 2020 Share Posted June 7, 2020 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 1 Quote Link to comment Share on other sites More sharing options...
Backfire Posted June 7, 2020 Share Posted June 7, 2020 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. Quote Link to comment Share on other sites More sharing options...
Marvel Posted June 10, 2020 Share Posted June 10, 2020 . Just looked at the schematic again... Quote Link to comment Share on other sites More sharing options...
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