Jeffrey D. Medwin

I don't know for sure, but I would primarily blame the amps typically that people run. On any good speaker, you hear all the flaws of poorly executed amps, and most amps I see and hear are compromised in their execution. A high efficiency speaker will throw it back to you - " in your face " !!! You get to hear their electrolytics, ( sadly bypassing the cathode resistors, and / or, in the main power supply ), instead of good film caps. You get to hear other design mistakes, such as often-employed capacitor-input-filters, and almost always, inattention to wiring, ........ on and on. Makes listening a boring chore rather than a wondrous pleasure. Probably 98+ percent of tube amps, ever made to date, use simple UNregulated supplies to their front-end stages. This degrades DICTION on voice. It is possible that only Audio Research Corporation includes some form of B+ regulation, to the front end of their amps, or, preamps . ( Wm.Z. did this from the beginning, on my 1968 Peploe Industries Dual 100, it had a separate tube- regulated 88 pound power supply chassis, and a 45 pound audio chassis. I have not studied A.R.C's recent schematics for years, but I believe active single or double regulation is the case). In 1982, my first triode from scratch design and build, used DOUBLE active B+ regulation, to the front end stages. My audio Mentor, Mr. Fulton, INSISTED I design it that way. The amp was fabulous. After that amp build, I slacked off, and used either no or " single " B+ regulation on my succeeding DIY amps. However, in this Forum-covered 2019 KT88 SE DC amp build, I used DOUBLE series SHUNT regulation, for the front end stage's B+ , and the " special listening experience " of understanding ALL the spoken / sung diction was heard again - in spades. This level of audio performance, I had not heard ANYWHERES in audio, ever since building my 1982 amp !! My comment is : if your amp is not double series B+ regulated, it will not ever do a voice PROPERLY, and if it can't do a voice properly, that is perhaps part of what you cats are hearing and calling " sibilence". The amp can't finely differentiate the signal, and the garbage, as well as it needs to be done. But then, active double series B+ regulation, is just ONE design consideration, I can name numerous other poor tube amp design areas, common in 99% of existing tube amps, that degrade music playback performance. Its a sad sad state, how poor tube amps that the public accepts as "good" are, VS: what is possible to have for music playback. Well, there you have it, like it or not. Now you know why I design and build my own amps, since 1982 . Jeffrey Medwin

Maynard, Look at how the Altec 345A amplifier's power supply PSUDs !!! Pentodes are insensitive to ripple on the B+ / plate, and the ALTEC EEs took advantage of that, used small capacitance amounts. Notice, from Mike's previously referenced schematic, the grid stoppers on the Finals, NOT the usual 1,000 Ohms, but instead, a more artistic 100 Ohms. Stock amp sounds good !!! Jeff

Good point . Thanks.

I'm sorry. It was early Sunday morning, and my reading time was very limited. I had volunteered to help a young girl, confined to a wheelchair, by picking her up and driving her to church services with me. Time to post was short. Its shades of the January 1. 1956 Columbia LP / OL 5090, from the Broadway play " My Fair Lady ". The song that comes to mind is .............................." Get Me to the Church on Time ". Jeff Medwin

I din't read all of the above, buy the first step IMHO is to swap the tubes, one at a time, but eventually all four, left to right and right to left. Does the buzzing go to the other channel ?? If so, there is likely no amp problem at all, but rather, just a tube problem. If this is the case, with only two tubes per channel, it will be easy for you to locate the bad tube, and then, replace it. Wait at least 5 to 10 minutes after shutting down amp, for the tubes to cool, before handling / switching them, and use a towel or a rag when pulling them. Relax and hang in there, and be cool headed. Jeffrey Medwin

Joe, If you can locate the bias resistors to the Finals tubes, that go from the Final's tube's cathode tube socket pin, to ground, you can determine the bias from Ohm's Law. Voltage reading at that resistor's end which connects directly to the tube socket ( amp at idle, on its side, bottom cover off, be careful, lethal voltages exist ) divided by the the cathode resistor's resistance in Ohms, ( measured when the amp is OFF ) equals the current being drawn across the resistor, stated in Amperes. Convert your division, Amperes computed result, divide by 1,000 into into Milliamperes. I don't know what type of Finals tube you are using. But you could go on line and download a tube data sheet which will show you, which pin on the 8 - pin octal socket is the Cathode , which may be designated on the data sheet as " K ". - - - - - - - - - - - - -- - - - - - - - - - - - - - - - - - - - - - - - - - -- - - - - - -- - - - - - - - - From a general perspective, our listening experience with Dyna Mark 3 based amps ( Paoli 60Ms, etc. ) over the years was such, that we never kept them, longer term. But YMMV. If you,, or a trusted local friend has a very good DIY capability, I can suggest a few simple conservative mods, that keeps the basic Curcio ( Dynaco, Latino etc. ) circuit fully intact - yet will nicely improve it ( better definition and much better dynamic contrasting ). Parts cost, exclusive of shipping, is $12.00 to $21.00 for both amps. Jeff Medwin

Take this from a fellow TVIX trader, ( Dowto1000 on stocktwits ) use 12 AWG, do it as good as you can.

Personally, in my system, for L.P. playback, I like having very precise control over volume levels, and balance. This precision control is only obtainable with a potentiometer, but its got to be done as a very very well thought-out implementation, using top-quality parts. That is my next DIY build effort, to rebuild my Resitive Attenuator, with better parts and a more flexible switching capability, and likely add phase-reversal of sources. I hate to switch speaker leads at the amp, to hear out-of-absolute-phase recordings properly played back in my listening room. My 1978 Fulton dual-mono Bravura preamp, in addition to a normal volume control, also has a FIXED output of phono, with new RCA jacks installed. FIXED out totally bypasses the Allen Bradley Mod Pot balance and volume controls taken from the output of this unit. I want to hear that - next. Take the phono signal, " FIXED out " - no internal-unit attenuation, into a rebuilt highest-quality external Resistive Attenuator. This Bravura phono unit used a nicely-designed P.C. board, with large ground areas, and wide traces. One of the many things Mr. Fulton did back them, was to HEAVILY modify the board's traces, with real wire. Can you see all the green - colored wire he added in parallel to the board's traces ?? Wonderful transfer efficiency, and this unit, using a directly coupled passive RIAA, very nicely performs !!

Hi Mike, An ALTEC 345A is a very special amplifier, circa 1959. Good sounding !! It has Peerless iron ( Altec owned Peerless ) and thus - lovely output XFRS. The circuit is unusual also, as it has a separate G2 supply, for the EL34s, and although run as a pentode-like tube, the voltages on the G2 are triode-like !! Its a very good sounding amp, and quite desireable to own. By no means would it go cheap on resale, say on eBay !!! Notice it has two 5U4GB tube rectifiers which is exactly what I chose to use in my 2019 SE DC KT88 amp. 345As are COOL !!!! Its only design flaw was that one bias pot adjusted all four EL34 tubes. A common 345A modification was to use individual bias pots, to adjust each tube on its own. In your picture, you can SEE where two red, and one black voltage sensing jacks were installed, for each channel, to monitor output tube bias, on an individual basis. Jeff Medwin

Why not! Micron level is not possible. 3.5 inches all, or even 1.75 inches all, if they would reach and its do-able. Jeff

Mike, I enjoyed seeing that photo / DIY execution. I feel Dave's Autoformer, being in the front-end of the system, deserves to be housed and executed much much better than that we are seeing in our posted photo. Consider this, it resides at the beginning of the system, and ANY losses of fidelity, that a DIY execution imparts, will be passed on the the rest of the system, and losses will never be made up at the speaker end !! Lets discuss a more ideal way to execute that autoformer, what I would want to do, if keeping it long term, for my own use : First of all, a single pair of RCA jacks in and out, as shown, is too limited, to only one source. This autoformer ( or any good resistive-ladder passive attenuator ) can eliminate the use of a Line Stage, in most perfectionist systems. So, a good passive Attenuator should do multiple Source - Switching as part of it's design. I would think, to give an Attenuator a minimum of three sources, one phono and two line inputs. The two best switches, sonically, I know of would be either the Shallco 10 A. silver switches from Michael Percy, or the Grayhill silver alloy contact switches,...... Grayhill Series 42, 43, 44 and 54 - shorting types only ( MBB , make before break ) . Anything else would likely be second best, and a degrade. This Attenuator will require more than one switch : one switch to pick taps on Dave's autoformers, and another switch to select sources. If I were building this for myself, long term use, I'd want the best RCA jacks. I would use Vampire RCAs, their top -of-the line directly gold plated pairs. CM2F/CB, also from Michael Percy, at $33.95 a pair. I would likely not use the press-to-connect clips we see in the photo, on each Autoformer tap, bit rather, ' would carefully solder directly to each of the 24 taps. Realize, since source signal levels are among the lower signal levels in the audio chain, I would only use the very best hook-up wire available, to build this. In my thinking, there is only two hook up wire choices to employ, both are pure silver. Cost is about $2.00 an inch. One choice would be Kimber Kable's lovely AGss. An alternative, would be DH Lab's Silver Sonic 18 AWG pure silver hook up wire. None of these individual hook-up wires should touch each other, and of course, twisting polarities is a No-No !! All my suggestions are just my opinion. Doing all of the above, no shortcuts, would be the best execution I am aware of, to get the most out of the basic Slagle Autoformer. Who in this world will proceed and do all of this first ??? Jeffrey Medwin

Thanks for posting !! I personally would be hesitant to use that as it appears to be a 71 Series Grayhill. I would only consider a Grayhill rotary with silver alloy contacts, for low level audio signal use, and also - only a shorting type of switch ( MBB or make-before-break ). Their silver alloy models are Series 42, 43, 44 and 54 . I've located some to do what you want, surplus priced. P.M. me and I will be glad to refer you to them, under $30.00 with shipping as I recall. Jeffrey Medwin

Respectfully, I find your comment above quite amusing. I don't care much about the science, or need any proof, just the result. Whats important to judge : temperature rise OR............. how does it sound? " Don't tell me about the pregnancy, just show me the baby ". Thanks for posting Glens, have fun with my posts if amusing, and - its very nice to meet you. Jeff PS : Remember my first Audio Mentor's commentary " Scientists don't pursue the truth, it pursues them. " ............1978 .......................R.W. Fulton

You are correct .................in as far as you went. I am not merely suggesting plated switches sir. The plating occurs in the less costly 71 Series switches, plated with nickle, silver and gold, as per their datasheet. These 44 Series switches are all silver switches, described in the datasheets, not as plated, but rather as a silver alloy. Additionally, I get supporting confirmation, ' have two very experienced and trust-worthy high-end audio Manufacturers who vouch for these the Shallco and Grayhill 44 Series silver switches. Thanks for posting ! Jeff

Please tell us, how do YOU know how much wire is necessary , to play back audio information and be faithful to the music, and be able to comment on it, and tell us what is needed as you do?? With this Mil Spec wire, over the last five years, 16 AWG has been a decent compromise, between retaining the highs, doing the lows AND having the dynamic expression on music play back. 14 AWG is not bad either. " Retired time ", not quite. Today is just my day off. I am 75, need to work, and intend to ( hope to ) do so for another seven more years. I take time with audio because its important - to me.