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I have a Magnavox with a pair of EL84's for the output that I use with my MacMini Desktop computer. Sound is fantastic. Pic and what I believe is the schematic is attached. I've replaced C6, 7, 9, 10 caps with some yellow KimberKaps I had, plus the electrolytic can with new cans mounted under the chassis. Any simple suggestion that will further enhance its performance would be appreciated. Thanks in advance.
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here is mine i use it in the office ,most caps and resistors changed ,i wires a volume control and also used a ac line filter before the rectifier tube they like speakers in the 4 to 6 ohm
spent maybe $50 max and felt that was it nothing more left to improve besides nice nos tubes
What is the purpose of the heat sinks sitting on top of the Power Transformer? That much of difference, or just a whim?
yes when using in summer months they run hot and i have measured the temp to over 105 degrees with the heat sinks the temp drops to around 100 and in my past experiments and experience usink heat sinks and fans have helped prolong the life of my amps
i have a dynaco st35 still original with the last change of power tubes 18 yrs ago its still plays on spec and sounds awsome, i use some computer fans with old cellphone chargers the dynaco does not even get up to 85 degrees
i just retired my 3 altec 1569 amps from my home theater and these monsters ran for 20yrs with no problem
heat is the enemy for reliability as for sonics maybe 0.5% better on high end equipment
My guess is that the power supply is underspeced and gets hot.
Dave
It sure does look nice!
Dave
I am not familiar with this particular unit, but from the pictures, schematic and discussion, it appears to be a very marginal piece of gear.
It is not obvious to me why anyone would bother with it. Would someone be kind enough to explain?
Well, my main system utilizes an ARC LS17SE preamp, HK Cit II rebuilt tube amp by Mike Samara, and Merlin TSM Black Magic speakers. So I have a reasonable understanding of what better equipment sounds like, along with my performance background as a musician. Picked this EL84 amp up off the curb for free in the original cabinet (which was returned to mother nature). I utilized it originally in my work shop and now for near field listening (~3 ft) with my desktop computer. I'm simply taken back by the sweet sound of those EL84's - for something that is sold old and basic. So if I can toy with it to get a little better sound out of it with parts I have lying around, I'll be very happy. Not going to spend $100 dollars on it. But it does cause me to look more closely at EL84 amps. There are bigger versions of this type of amp that folks completely rebuild and utilize.
I had a few EL84 amps "back in the day" -- I recall Fisher and EICO integrated stereo amps and, earlier, a Heathkit UA-1 or 2 mono power amp. These amps well designed, made with quality components and, yes, sounded sweet with efficient speakers.
I thought enough of the Heath that I used it with a McIntosh C8 preamp and an Altec/Karlson speaker system. I also recall a belt drive turntable and many hours of good listening.
It seems to me that what you are doing with the Magnavox is equivalent to polishing a turd, but if you like doing that and the way it sounds, by all means...enjoy!
That sound like a very nice system. I see you have went quite a different direction with you current system. I too have switched from tubes to sand amps, and am very happy with the sound. However, I do look back at my tube gear with fondness. It gave me many hours of music enjoyment!
Dave
For about 25 years my tube gear was all McIntosh -- MC225, C11 and MR65B. It was becoming a maintenance problem. Then Mac informed us tube gear owners that there were not able to resupply certain preferred components, and could no longer guarantee that they could repair to original specs.
I had bought some solid state stuff to back up the Macs in their anticipated trips to Binghamton and liked it enough that I decided to declare a personal end of the tube era. I don't miss banging on preamp tubes with pencil erasers, but still have fond thoughts of that MC225.
I understand the maintenance issue all to well, and I can work on the equipment. I really enjoy the sound of my system, but I will be dabbling it tube gear. I have a few pieces of tube gear on the shelf.
Dave
It may have a asthetic that some might not like, especially this is a console pull. But a lot of these amps, when overhauled and brought up to spec, sound pretty damn good for what they are and what little ( I least in my experience) people pay for them. With th ebay prices going nowadays and a revival for "midcentury" console being the hip thing now, the prices some of these consoles are demanding are laughable, at best.
If you are handy and enjoy diying and tinkering, they are a great, affordable way to get into tubes.
Oh, and they sound great for what they are and you have to put that into prespective. My first one was a VoM 6v6 console pull , then I went crazy and had about 10 of these laying around in different stages of repair. I used these on my old 604's and enjoyed my music on the cheap, very cheap......
Absolutely. These gems can't be overlooked.
I have quite a few console pulls that have been brought back to life...some with mods. I like them all. They are the only amps I run in my office.
My other amps? Jadis Defy-7, McIntosh MC275, and a slew of vintage tube amps.
The console pulls get 90% of the airtime.
"I can't compete with the dead". (Buck W. 2010)
Do something to improve the AC delivery. Upgraded hardwired power cord. Even very low current devices improve a lot when this is addressed.
E
T
Perhaps you should also consider a power transformer salvaged from an
MC30.
EL84/6BQ5s don't need a lot of driving.
IF that bothers you and IF the heater current reserves in the PT allow, you could try a lower gain twin-triode.
Warmest
Tim Bailey
Skeptical Measurer & Audio Scrounger
No problem with gain.
Just thought there might be nice tweak unknown to me that would up it's performance.
C6 and C9 are for bass boost, probably unwanted if the amp is used stand-alone. The gain EQ was to compensate for cartridge, speaker, passive tone controls. The bass control does nothing unless it follows a ceramic cartridge, treble is high-cut only.
What surprises me is that Magnavox and others with these little SE did not repackaged them along with the front end as tuners, tuner/preamp and preamps. Even back then these little components were pulled as the consoles were trashed. Considering the sales of the ST35,little EICOs and the Scott, Grommes, Sherwood, and Fisher EL84 amps, there was an obvious market. I know it was explored at McIntosh but nixed, being fearful it would just eat into the MC240 and MC225 sales. It would have required from a marketing standpoint an inexpensive preamp and tuner or combo unit. It could only be justified if it was incorporated into a receiver and Frank hated that format. A dealer survey showed this lineup was more than welcome but went no further. As McIntosh was not located in a major market like Boston or NYC, Mc tuners needed pulling power. So, Frank killed it. Of course, this was a bad assumption as proven by almost all other tuner producers who could come up with simple,easy, inexpensive designs. He also did not recognize if persons saved on the preamp and amp, there was more interested the budget for his level of tuner. The joke was his tuners save the MR78 and MR71 of the times were no better than an average tuner from other companies. Frank sometimes lived in a land of fancy.
Don Brian Levy, J.D.
Toronto ON Canada
I question your assertion that the Mac tuners were "no better than an average tuner from other companies". Their first, mono FM-AM tuner was a disappointment, but the George Merkel designed MR65 redeemed them.
In the mid sixties I set up at my home near Binghamton a 50 foot mast, Finco FM-5 antenna, rotator, UHF spec (unshielded) leads, etc. Among the tuners I tried were Scotts, Fishers, Sherwoods, Pilots and Macs --specifically the MR65B and the MX110. A surprise performer was a little Eico mono tuner (I think it was the HFT90), but the best overall balance of sensitivity and selectivity in my location was the classic MR65B. That was the keeper for me.
One example I recall: WQXR broadcast at 96.3, from the Empire State Building. A few miles south of me, in Montrose, PA, in line with WQXR within the beamwidth of my antenna, there was a religious station, WPEL, broadcasting at 96.5 with -- if memory serves -- 100,000 watts. The MR65B was the only tuner I tried that consistently would pull and hold a clean MPX signal from WQXR off this strong adjacent channel.
I do not recall consideration of McIntosh making anything like the Magnavox "receiver" described here.
Regards.
briggs
I have rebuilt & upgraded these amps. I used K40Y-9 at C7 & C10. I used silver mica at C6 & C9. I rebuilt the power supply with a JJ 40-40-20uF @ 500 volt capacitor. At C1 I used a 100uF Elna Silmic II.
Tube rolling won the Mullard 12AX7 long plate & Sylvania 6BQ5 black plate.
Confused. I have a 6EU7, two 6q5's, and one 6ca4. Where are you putting the 12AX7?
6EU7 and 12AX7 are about the same tube inside the bottle. Both are twin triodes with a mu of 100. The 12AX7 has a center-tapped 12 volt heater so it can be run on either a 12 or 6 volt heater supply. The 6EU7's two heaters are in series and need 6 volts.
So you'd have to rewire the socket to use a 12AX7, but that's it. Also, if you rewired for a 12AX7, you could try a 12AT7 (mu of 60) to see if that sounds better to you.
My version used 12AX7. Best 6EU7 I heard are Raytheon.
Some of those did use a 12AX7 (obviously not the one that the OP has, though).
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