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Author Topic: Valve amp designs Will Kutler Phenomenal Film Handler Posts: 1506 From: Tucson, AZ, USA Registered: Feb 2001 posted 10-08-2005 01:45 AM                     Hi Mark As part of my RCA 816K restoration, I needed to remove the selector switch/oscillator coil assembly as a unit to facilitate a necessary repair to one of the open wafer switch contacts. Anyhow, the assembly was extermely dusty and dirty, and alot of crap was imbedded in the protective wax used on the many oscillator coils. And all that original wax was nothing more than an oooey gooey mess! Using a heat-gun on low, I was able to start cleaning up the coils. But I need to recoat them and was strongly considering Q-Dope. Now Q-Dope is rather expensive, and is nothing more than pure polystyrene dissolved in solvents. And polystyrene HIPS is commponly used as an electricaland thermal insulator. Styrofoam is polystyrene. So, what is your take on dissolving Styrofoam in acetone and dipping the entire coil? Or do you have a better suggestion? I am aware of the importance of keeping those coils dry: that depending on how and what they are coated with can eventually cause problems. Cheers K  |  IP: Logged Luciano Brigite Master Film Handler Posts: 277 From: Sao Paulo, SP, Brazil Registered: Jan 2002 posted 10-08-2005 10:43 PM                     It took a lot more time than I thought to look tru my stuff and find a schematic closer to what I described here in the previous posts.the only thing different in this one is the EF86 in the input and the OPT has only a 16 ohm output. take away the EF86, replace with a ECC82 hooked up for line level and a OPT with a 6.600 ohm primary with screen taps @ 43% from the center tap and 4/8/16 ohm secondary. I wanted to draw my version of it but I'm getting worse and worse in drawing schematics Mark asked about a response test of the transformers, well I hooked my portable RTA to the amp. and fed it with pink noise, this is what I got from the entire system ( amplifier circuit, transformer and speakers): and now this is what I'm using to "make noise" at home .. ( didn't come out as I expected but isn't a total loss either. the power supply output goes way down when the 6L6s heats up and starts working. 5R4 sucks  |  IP: Logged Paul Trimboli Master Film Handler Posts: 274 From: Perth Western Australia Registered: Dec 2002 posted 11-08-2005 04:48 AM                     Luciano how to do you find your home made transformers? I know most of the factory wound units use interleaved windings, I am guessing you could not do this at home so how do you find their hi end response? What sort of winding rig did you use? Where did you get the core and iron from?  |  IP: Logged Paul Trimboli Master Film Handler Posts: 274 From: Perth Western Australia Registered: Dec 2002 posted 11-08-2005 07:56 AM                     Just was reading through the post again and noticed you mentioned that you did interleave the transformer windings, I would be interested to read more about this.  |  IP: Logged Bruce McGee Phenomenal Film Handler Posts: 1776 From: Asheville, NC USA... Nowhere in Particular. Registered: Aug 1999 posted 11-08-2005 08:16 AM                     I havent seen a 5R4GY like that in years. Is that NOS?  |  IP: Logged Luciano Brigite Master Film Handler Posts: 277 From: Sao Paulo, SP, Brazil Registered: Jan 2002 posted 11-08-2005 05:35 PM                     Paul, I found the interleaved winding easier to do than a normal,continuous winding for primary and secondary.Sure it have it's tricks and since those two transformers shown were the very first ones I made using that kind of winding I got very surprized with the results, and all of them including the power transformer were done by hand, no machines or anything to do the winding, of course they didn't came out in a few hours, took me about a month to complete each OPT and a week for the power transformer. There is no "esoteric" material in them ,enameled copper wire is the kind used in most of consumer transformers and the iron is of standard laminated steel ( not the GOSS kind wich costs a lot more) insulation between the primary/secondary layers are done with off the shelf white paper and the bobbin (winding core) is the formed plastic. the lamination is not crossed ( like E-I,I-E, a little hard to explain it on text only)but stacked with all the "E" to one side and the "I" to other and a piece of paper or plastic between them for the core gap since it's a single-end OPT. From what I could see with htese transformers, the frequence response is based on the core size ( for low to mid frequencies) and hte number of interleaved windings (for low to high frequencies) a bigger core gives more bass and more interleaving,mids and highs. sure it has limitations and after some point it doesn't do any better to any side and makes things only more expensive and complicated. The interleaved winding design I did in these transformers were based on information from the " radiotron Designer's Handbook,4Th edition" and also from taking the covers off of a transformer and taking a look at how the winding was done of course *without* disassemble the whole transformer and undo the winding,most of them will show where the windings starts and ends and wich one is primary and secondary. Mine has a primary in 10 layers connected in series interleaved with 8 secondaries in parallel.finding out wich wire to use in hte secondary is one of the tricks here, since it has to be done in one layer htat'll fill the heigt of the plastic core without leave an empty space at the end of the turns nor overlap them to complete the requested number of turns. the same number of primary turns in each layer is also important. I have two other OPTs on the way,htose however went in halt mode because the secondaries doesn't fill the entire heigh,messing up with the next primary layer. when time allows me, I'll get back to them,redo the winding math to fit the core I selected and take pictures of how they're being done. ( I'm extra busy with theatre work this month,but I'll have something about them as soon as I can) Bruce, that one is a JAN 5R4WGA and yes, it's a NOS, made by Chatham,in 1956 if I remember it right. I have some 3 more of those somewhere along with some 5Z3.  |  IP: Logged Phil Hill I love my cootie bug Posts: 7595 From: Hollywood, CA USA Registered: Mar 2000 posted 11-08-2005 05:43 PM                  Hiya L! You might wanna post an accurate schematic as to what you built as the above one is a pretty crappy design...it's riddled with poor engineering. Also, I'm sorta disappointed at the BIG dip at 31 Hz, but without a true representation as to what you've built, we cannot actually comment on it. While the 5R4 is a great tube for SOME applications, it's not for what you're using it for. At the very least, a 5AR4 would be better. Bruce: There are plenty of 5R4WGB ruggedized rectifiers with the hi-temp base and thick glass envelope available.  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 11-09-2005 08:03 AM                     Phil, You've got it all wrong.... Even those ruggidezed 5R4 rectifier tubes are weaklings compared to a decent mercury vapor rectifier tube. Aside from handling a ton more current they also look way cool! Mark  |  IP: Logged Luciano Brigite Master Film Handler Posts: 277 From: Sao Paulo, SP, Brazil Registered: Jan 2002 posted 11-10-2005 07:24 PM                     The dip at 31Hz is a mistery to me ,no idea why it's happening. hte only thing I can relate to it is that while doing the math for core sizes,a work frequency is requested and I have used 30Hz for every OPT I calculated.. I got the 5R4WGA along with a lot of oddball tubes, most of them seems to be lo power transmitter tubes ,some Russian tubes and a few Philips SQ tube types.there are some mercury rectifiers in the boxes,but I have yet to find a place with tech data for them ( and before that, the list with the tube codes. ) My intention was to use a 5U4 and not the 5R4..  |  IP: Logged David Buckley Jedi Master Film Handler Posts: 525 From: Oxford, N. Canterbury, New Zealand Registered: Aug 2004 posted 11-11-2005 12:10 AM                        The 31Hz dip, does your RTS allow you to measure the amp output electrically? Have you tried the two channels independently? Could be a room thing, or height of speakers off floor...  |  IP: Logged Luciano Brigite Master Film Handler Posts: 277 From: Sao Paulo, SP, Brazil Registered: Jan 2002 posted 11-12-2005 06:26 PM                     David, my RTA can read frequency response electrically ( balanced line level),I have to make a connection cable for this use, since it doesn't come with any. The test I showed was made with both channels at same time, fed by the RTA's generator and sampled by it at a distance of about 4Ft from the speakers.Those aren't big speakers and are in my computer desk's shelf. It still surprizes me because,for me, the bass response is performing well.  |  IP: Logged

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