slow death spiral

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Re: slow death spiral

Postby Quad » Tue Jun 25, 2019 4:01 am

mesherm (Mike Sherman), I am so happy to see your post - it has been a
long time since we have seen any post from you. The "Advanced Snake Oil" thread you started
has had such a long life :)
The tiny Amplimo toroid build you posted here was cool (pics below) and inspiring and I got a VTA board from
you to build my first tube amp with Trafomatic toroid OPTs.

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Re: slow death spiral

Postby kheper » Sat Jul 13, 2019 6:34 pm

Can we attribute diytube's "slow death spiral" to the evil monstrosity that is FaceBook? (I know I'd like to.)
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Re: slow death spiral

Postby jwhitmor » Wed Jan 15, 2020 5:19 pm

I still enjoy diytube. Like the others, I am sometimes too busy to build equipment, but I still have the tools, and parts to do it. Shannon Parks and Tom McNally have done an exceptional job of running the board(s). I learned a great deal from everyone that posted here; questions, and answers, photos, and information. Diytube fills a very significant gap in tube audio. At the top are the very nice, but way too expensive, commercial offerings. I always wanted to own a tube amp from Audio Research, but the family needed a roof over their head more. Then at the bottom are some Asian imports, where many compromises were made to get the parts cost in line with the shipping cost, and to satisfy the budget market. Here I got information and printed circuit boards to build equipment as good as my ears. Shannon has a recent video where he answers questions. He said that, "someday" he would like to get back to this type of interaction. Someday may never come, but I hope most of us are still here if it does. 2355 registered users are not wrong. This is a great pursuit for those who are interested.

For the record... I have no Facebook account, and I never will. (evil)
If it is not making X-rays, your B+ is too low.
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Re: slow death spiral

Postby jwhitmor » Fri Jan 17, 2020 10:24 pm

OK, maybe 2000 of the registered members are - EBAY tube sellers - but that still leaves 355 of us diehard enthusiasts.
If it is not making X-rays, your B+ is too low.
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Re: slow death spiral

Postby dannyr » Tue Jan 21, 2020 2:23 am

I just figured that facebook groups hurt this place. Most forums that I go to are all ghost towns these days:(
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Re: slow death spiral

Postby jukingeo » Sun Mar 21, 2021 2:17 pm

Hello All,

I was going to create a post like this myself, but noticed this thread and decided to chime in. I have a returned here a week ago as I was dusting off some of my old planned tube amplifier projects that I have started many years ago, a couple being just over a decade now. The reason for my long hiatus from completing my projects was due to a few moves, the death of my parents and bringing up twin boys. The latter was the primary reason why I stopped working with tubes as I didn't want any inadvertent "accidents" due to curious hands. But now my sons have reached 14 years of age and they are taking on responsibilities and they know if I say not to touch something, they don't touch it. So I figured I could get back to some of the lower voltage and current tube amp designs.

Low and behold when I returned here to diytube last week, it seems that the site is a former shell of what it used to be. This used to be the go-to site for many single ended amplifier projects. While I have received help from many here, obviously the two big standouts where Shannon Parks and his amazing PCB's and of course "reference" builder Tom McNally. Between the two of them (and again those that have helped me in the past), I was assured that whatever I would build would be a success, not only electrically, but sonically too. Coming back here now, it seems as if the two tube amp greats have disappeared. Further, Shannon has stopped producing his PCB's. It seemed that activity here slowed down from 2016 through 2018 and now, as some pointed out in this thread, Diytube has become a ghost town.

I am curious to know what happened? Why did Shannon stop making his boards? Where did everyone go to? I know that Tom is still making his amplifiers as his website is still active, but I don't know where he is 'hanging out' now. Further, what happened to Shannon?

Is there another "go to" diy tube site that came out and everyone is there now?

A big worry of mine now is how much longer this site will remain up. There is a wealth of information here that would be a shame to see that it is lost. Granted I could go to Tom's site directly for assistance, but when I had posted a question here, sometimes I got my answer through someone else as I felt a bit awkward going to Tom all the time. I remember a fellow by the name of Ed Brown and he was another big help here. I have not seen a recent post from him here, either.

I had also noticed that the forums are closed to new registrations, which has me concerned if Shannon is no longer moderating the site.

So I am curious if anyone could give me some information as to what happened here between 2016 and now. Further, I would like to know where everyone went?

I have seen some posts on the DIYAudio site, but nothing that seemed like everyone went there.

I know there seemed to be a hint about Facebook, but really? In all practicality you can't really find information on sites like that. God forbid you want to go back and track down an old thread...you can't do that there. So I don't think that could be it. But I know I could be here and stab at possible reasons all day, but it probably is best that someone in the know (here) could tell me what happened.

Thank you,
Geo
Exit Light, Enter Night, Take My Hand...We're off to Never Never Land.
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Re: slow death spiral

Postby AmadeusMozart » Sat Jul 17, 2021 7:55 am

This was one of the most enjoyable boards - other forums I have visited invariably are populated by younger people, who have not studied the basics and are know-alls. When pointing out a flaw in their reasoning the responses normally get unpleasant.

I've been busy with other things and we moved late last year to a part of the country that is safer for my health and where we are closer to out children and grandkids. But I've been busy with chores around the home and once those are finished I'll be building my last amplifier. I've been pondering, modelling and finally came up with a design I like.

FWIW I always liked the Budgie and in a moment of insanity I sold it to fund a clone of the Audio note Kit 4 which in itself was a clone of the Sansui HF-V6K from 1955. It did not stack up to its reputation and no Budgie PCB's were around. So build myself an UL EL84 with the 5670 as a driver unsing all Transcendar iron. Gery (Transcendar) has now closed shop (retired) and I anticipated it and bought two 10 watt SE OPT suitable for El34 / SEP EL84. (jumping for joy that I did itat the time)

But I made a mistake with the design for the SEP EL84 and bought the wrong power transformer. By chance I happened to find a deal on a pair NOS EL506 which were the first output tubes I bought for a PP amplfier when I was a youngster. Brimar made these tubes and they are a Magnoval version of the RCA 7868 which has a Novar base. I also ended up finding a quad 7868 here in New Zealand with known provenance coming from a shop I frequented many years ago. Last but not least I also bought a pair from a "reputable" seller in the USA who turned out to be more or less not that wonderfull. Supposedly matched - NOT! As a result I have four pairs.

The 7868 / 7591 / 6GM5 /EL506 are all very, very similar except for a different base. The Electro Harmonix 7868 is a close copy of the EL506 (has a magnoval base - don't use them in the Novar socket, you'll crack the tube plus some other things need to happen: they have a far lower grid resistance and bias differently).

Anyway, back to the original 7868 / 7591: these are basically the cathode / filament of the EL84 put into a larger envelope with a larger anode and instead of having a screen they are beam power tubes. A beam power tube has less H3 and more H2 distortion than a pentode but uses less screen / beam plate current. The 7591 was used in the past in great quantities and largely went into obscurity since the guitar players had no interest in it since it was a purposely designed HiFi tube with a 19 Watt anode dissipation and often driven far beyond that. It was one of the last mid power tubes to be developped for the home market (30 / 40 watts in push pull).

At 300V it models very similar to the EL84 (6BQ5) and if you have a 6BQ5 running on its toes then you can replace it with the 7591 / 7868 and exerience a far longer life.

I've come up with a design that only uses local feedback in the output stage yet I achieve around 1% distortion at onset of grid current. At 1 watt it has less distortion than if I was to use global negative feedback. Less or no Global Negative Feedback results in less IMD. No PP results in no crossover distortion or non-linearity due to the hysteresis of the iron in the OPT. Reports on amplifier with CFB have been a long oputput tube life and a life like reproduction with the right speakers.

I do not need lots of output power next to my computer but I like a long life of by equipment so the tubes are not running full tilt and I expect a minimum of 10 000 hours out of the output tubes and I have read reports of achieving 20 000 hours for the 7868. Because of the octal socket the 7591 cools differently and has a slightly shorter life expectancy.

It took me nearly 9 months off and on modelling, hopefully the implementation is close to the modelling. But I expect some tweaking may be required as output transformers do have an impact, I have acquired a HP 339A distortion meter that was in bad shape and needed resurrection. I also have a Focusrite 2i2 that I will use with REW for spectrum analysis and bode plots.

The power supply will have some thermal relays - one after 45 seconds to cut out the NTC resisitors in series with the primary and then 15 seconds later the NTC resisitors in series with a 6CL3 damper diode will also be bypassed. Boththese steps improve the life expectancy of the tubes. (slow switch on of filaments and slow rise of B+). Drivers are two Brimar E81CC in SRPP with values selected to match the non-linearity of the output tube (and hence making it more linear since that is in opposite direction). (Brimar was an American company (it may have been GE) trying to break into the European market and close attention was given to trying to produce only the best quality).I've also got a pair of NOS Mullars ECC81 and a sleeve (5) Telefunken ECC81's so set for life.

Unfortunately the OPT is a special item, custom made. The secondaries may be 4,8 & 16 ohm but they were made in three separate windings with only a small part of the 4 Ohm winding common. (after that first section the 4 , 8 and 16 each had their own interleaved parts).

There may be a custom winder that can wind one for you, sofar I have not found anyone interested/capable.

Still collecting some parts, waiting for some aluminium from landfall systems to arrive and then I can start on putting the chassis together. In addtion to running the tubes conservatively they will be receiving tube coolers to extend their life even more. NOS 7868 / EL506 are extreemly hard ($$$) to find and of the new vesions only the 7868 from EH come close but require the Magnoval socket. (I've got both NOS Novar and Magnoval with some spares ) Aiming to have it finished by Christmas but the color scheme is something that is giving me grief - cannot decide on what to do.

The UL / CFB is based on Quad and McIntosh ideas and I view this amplifier as the SE Quad that Quad never build. Output is between 5.5W and 7 Watt per channel depending on B+ and how hard the tubes are driven.

Cheers
AM
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Re: slow death spiral

Postby AmadeusMozart » Fri Nov 19, 2021 10:19 pm

Had some compression fractures due to osteo porosis so not much has been done. Some mistake with the chassis meant that it will have to be redone. Between the chores on the house (still not finished but getting more time between them due to delay's outside my control) I am slowly working on the chassis. Created a simple milling setup with an old portable drill and sturdy drill press so I can machine the top plates for the chassis. One part will hold the power supply and the second top plate will hold the amplifier. The PSU part will be fixed to the sides and the amplifier part will be removeable. In this way the amplifier can be modified: either have a changed setup (different tubes, different output transformers) or a different layout. Cooling of the tubes will be an important part.

Regarding slow death spiral: This is not only the case on DIYtube but there is also noticeable less action in the tube sections on AudioKarma and DIYaudio compared to some years ago. More and more substandard and badly designed C***se cr@p is being bought and then $$$ NOS tubes are being put into those. Grrrrr..... the waste of good NOS tubes. But don't tell the new proud owners of these amplifiers that their new amplifiers are not representative of the high end older US / UK made gear. The polarisation and abusiveness introduced by the previous president is surely going to be on display afterwards. I've stopped posting on both websites (and also on audiosylum).

I've stocked up on the parts I expect I might need to maintain the two amplifiers as I do not expect that current supplies will stay around due to deminishing demand. Still in two minds if I shall order some Hashimoto output transformers. Having said this with Covid being released in our country (lockdowns are going to be lifted) and my immune problems the need for new OPT may be academic.

To those that are relatively new and want to get involved in vacuum tube gear: remember you are working with lethal voltages, study the Radio Designer Handbook and do not listen to what is currently being spouted on the forums. Old postings (10 years and more) are still valuable but nonsense and ego have taken over resulting in more useless misonformation than usefull practical information.

Go well my friends, thanks Shannon for the friendly website, I've enjoyed being here. Hopefully I'll be able to showcase my new amplifier here at some stage in the future.
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