thebes Posted November 16, 2014 Share Posted November 16, 2014 (edited) $38! Why your practically throwing money out the window. OK I understand your comments about the Edcors, but I sure did like the cake-pan SEP so I guess I would prefer it over a SET build. I do have a question about the output transformers. These Edcors: https://www.edcorusa.com/gxse10-8-2_5k appear to go lower than the Hammonds, are a third cheaper but are rated for 10 watts with 120ma max. Would using them necessitate a wholesale re-work of the schematic and parts list? Just think, with only three or four hundred emails to you I could have this built. Still mulling this over. Mostly what aesthetic style of build I would want, since I already know the circuit would be great sounding. I also would favor the variable circuit tone-control, it would be great for experimental purposes. Edited November 16, 2014 by thebes Quote Link to comment Share on other sites More sharing options...
tube fanatic Posted November 16, 2014 Author Share Posted November 16, 2014 $38! Why your practically throwing money out the window. OK I understand your comments about the Edcors, but I sure did like the cake-pan SEP so I guess I wold prefer it over a SET build. I do have a question about the output transformers. These Edcors: https://www.edcorusa.com/gxse10-8-2_5k appear to go lower than the Hammonds, are a third cheaper but are rated for 10 watts with 120ma max. Would using them necessitate a wholesale re-work of the schematic and parts list? Just think, with only three or four hundred email to you I could have this built. Still mulling this over. Mostly what aesthetic style of build I would want, since I already know the circuit wold be great sounding. I also would favor the variable circuit tone-control, it would be great for experimental purposes. No reworking needed. The difference in the dc resistance between the Edcor and Hammond is only 50 ohms which is insignificant. If, by chance, the tubes you happen to use run a bit high in terms of voltage, we can simply adjust the value of 2 of the filter resistors. No big deal either way! At this power level, the Hammonds actually go very low with no problems at all; but, the price difference is certainly there. If it weren't for the blue color of the Edcors (which I don't like), I'd try a set myself. And I think the build would only require about 275 emails!!! :D Let me know when you are ready to order parts. I have some suggestions to give you for possible variants which you may want to consider. Maynard Quote Link to comment Share on other sites More sharing options...
mike stehr Posted November 16, 2014 Share Posted November 16, 2014 (edited) In the 50s, companies like Lafayette and Allied marketed cheap "phono" amplifiers using 2 to 5 tubes with series connected filaments. Unfortunately, they were plagued by 60 Hz hum issues, and had an electrically "hot" chassis depending on which way the plug was inserted into the wall (remember, this was in the pre-polarized or 3 wire plug days). Here's the RCA version, probably early sixties...I bought a cheap phonograph only console that used a ceramic cartridge. All the console contained was the TT, speakers, and this little amplifier. The power switch was set-up within the turntable. A single-ended 50C5 (pentode/beam?) job, with a 12AX7 driver. One diode for rectification, with some rather light filtering. The console had no fuse in the line cord. I tried this amplifier with my Cornwalls and a CD player...the amp does have a volume pot, balance, and a low to high tone control. It was akin to plugging the speakers directly into the wall socket, with some slight signal riding in there. Aside from the noise, it didn't sound too bad tonally I suppose... Edited November 16, 2014 by mike stehr Quote Link to comment Share on other sites More sharing options...
tube fanatic Posted November 16, 2014 Author Share Posted November 16, 2014 (edited) Here's the RCA version, probably early sixties...I bought a cheap phonograph only console that used a ceramic cartridge. All the console contained was the TT, speakers, and this little amplifier. The power switch was set-up within the turntable. A single-ended 50C5 (pentode/beam?) job, with a 12AX7 driver. One diode for rectification, with some rather light filtering. The console had no fuse in the line cord. I tried this amplifier with my Cornwalls and a CD player...the amp does have a volume pot, balance, and a low to high tone control. It was akin to plugging the speakers directly into the wall socket, with some slight signal riding in there. Aside from the noise, it didn't sound too bad tonally I suppose... 002.JPG That was the standard configuration for those little amps (the 50C5 is definitely running as a pentode, not triode strapped) as they were designed to be built into record player cabinets. Actually, if you build a low ripple DC supply for it, and replace the paper and electrolytic caps, you may be amazed at just how decent it sounds (besides being a whole lot safer to use!). Granted, the tiny output xfmrs will limit the bottom end somewhat, but it can still sound nice. Remember also that those old ceramic or crystal cartridges were often capable of a few volts output. The tone control was usually a variable RC filter in either the plate or grid circuit. Here's a more "deluxe" version which Allied sold in '56. It employs some neg. fb to get the distortion down: Maynard Edited November 16, 2014 by tube fanatic Quote Link to comment Share on other sites More sharing options...
Guest thesloth Posted June 27, 2015 Share Posted June 27, 2015 (edited) Not to get too far off topic but a way of cutting the price down for single ended designs is to go with a parafeed approach. You can actually use very cheap constant voltage (70v transmission line) transformers and get 10 watts out of them for full bandwidth. The transformers are like $5 a piece, drive a tetrode or pentode with source or cathode follower to get class A2 operation. To keep output Z and distortion low adding about 10-20db feedback is necessary. I can post some designs, usually the only trick is the output cap from the plate of the power tube and the inductance of the primary form a tuned circuit, it's easy to put the spike below the audible range, or use it as a bass boost Usually this cap from the plate needs to be somewhat large so it's okay use an electrolytic bypassed with a film. Edcor makes such nice iron for such cheap money I haven't been into the whole parafeed thing in a while. But if I were to build a cheap amp I am sure I could get at least 5-10 watts with a good dampening factor and good distortion for under $200. Edited June 27, 2015 by thesloth Quote Link to comment Share on other sites More sharing options...
tube fanatic Posted June 28, 2015 Author Share Posted June 28, 2015 Sloth, I agree that parafeed and use of a little line xfmr can be a good alternative, although the cost of a good plate choke negates some of the financial benefit. But, please post threads on any designs you have had success with. We all enjoy (well, at least some of us do!) stuff like that. Or, you can hold off for a bit in the hope that Chad will approve a new forum section for tubes in which it will be more appropriate. We can also get into some of the compactrons which have gained popularity in SE amp designs as well. Maynard Quote Link to comment Share on other sites More sharing options...
erik2A3 Posted June 29, 2015 Share Posted June 29, 2015 Sloth, we have discussed parallel or shunt-feed output topologies at some length in the past. I first joined the forum in 2002, and single-ended parallel-feed was one topic we visited often back then. I've also brought it up more recently. Good plate chokes, as Maynard pointed out, can be expensive, although in my experience the benefits in terms of sound quality over conventional single-ended designs offset the cost of parts required. I also once experimented with a combined interstage/direct coupled front end with parallel-feed output with grid chokes on the outout triodes instead of more common grid-leak resistors. I do recall one response to the parafeed discussions of the past where another forum member frowned on the approach because, according to him, the output transformers were too small to be any good....... Quote Link to comment Share on other sites More sharing options...
Guest thesloth Posted July 1, 2015 Share Posted July 1, 2015 (edited) Hey guys I am digging the discussions, and I think it could be a great thing if there is a devoted section to just tubes. Yes engineering is all about compramise and the parafeed surly has it's ups and downs. One way around the expensive choke is to use an active SS CCS. The choke does have the ability to swing the voltage above the supply voltage so when using a CCS you will have to increase the supply voltage. If anyone makes a comment on sound quality and the size of the output transformer the are just making a generalized comment, that may or may not be true depending on the design. Since you were discussing a parafeed amp then well they don't know what they are talking about. In most single ended designs the comment can hold some weight Most SE transformers need to be large because the air gap introduced in order to keep the core from saturating from the standing DC current lowers the inductance, in turn causing the low end response to be compramised. To get the inductance back they use a larger core and more turns so the transformer is physically larger and much more $$$$. I look forward to some upcoming discussions we will have. Maybe we can even have a community designed tube amp that is a good match for Klipsch speakers and our wallets Edited July 1, 2015 by thesloth Quote Link to comment Share on other sites More sharing options...
CECAA850 Posted July 1, 2015 Share Posted July 1, 2015 Maybe we can even have a community designed tube amp that is a good match for Klipsch speakers and our wallets What a great idea. There's certainly people with the know how here (NOT including myself in that group however). Quote Link to comment Share on other sites More sharing options...
mike stehr Posted January 5, 2016 Share Posted January 5, 2016 (edited) tube fanatic, on 11 Nov 2014 - 11:52 AM, said: I wouldn't mind playing around with a painted chassis, but have read that there are adhesion issues unless the aluminum is first treated with zinc chromate to prevent chipping. Powder coating is really cheap to have done and creates a very nice, durable finish. You can powder coat something as small as a chassis yourself at home. http://www.harborfre...stem-94244.html I worked a boat trailer manufacturer, and they did powder-coating. I do know that aluminum parts had to cleaned/washed and treated with zinc chromate prior to powder-coating, I don't know if steel parts needed the chromate treatment or not prior to coating. Larger parts, (like booms and tongues) were shot-peened. Some went to get galvanized, others to be powder-coated were cleaned/washed/dried and coated. I had a amplifier chassis done there, and they made sure I cleaned everything off of the chassis because they said it would need to be treated with zinc chromate for the coating to adhere properly and last. And it was a steel chassis. My only complaint is with gloss powder-coat finishes. It will get micro scratches...not so noticed with bright colors like white, but black...Yikes! Edited January 5, 2016 by mike stehr Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.