Magnavox 8601-20 how much can be crammed under the chassis

Discussion in 'Tube Audio' started by battradio, Oct 2, 2017.

  1. battradio

    battradio Electron trainer Subscriber

    Messages:
    5,513
    Location:
    Near ST. Louis MO
    This is what i have been working for a fellow AKer for the last week with a pause for the transfomers and chokes to show up .

    http://www.audiokarma.org/forums/in...ore-out-of-the-8600-series-a-lot-more.665735/

    The is based on David Gillespie's work , i modified the power supply with a second choke and a star ground for all high current ground . I also used parts on hand and changed the cathode resistors and pots to 100 ohms for or a total of 200 ohms adjustable from 100 to 200 ohms to set the bias .

    I moved the test points to the front of the amp using a 9 pin socket , i replaced the 9 pin socket with a better one with a shield and wired it for a 12AX7 instead of the 6EU7 . when rewiring the 6CA4 socket i broke a pin off and replaced the socket with a better used one

    I was double checking everything and noticed i switched the output wires , i'm used to everything as black to ground , that i did it automatically, will fix that tomorrow before i test it out .

    Have a metal shield to put between the second choke and the output transfomers if need be , .The second choke will have a near constant current and voltage on it , with the amp being class A so the magnetic field
    should be fairly constant .
     

    Attached Files:

    Last edited: Oct 2, 2017
  2. gadget73

    gadget73 junk junkie Subscriber

    Messages:
    32,922
    Location:
    Southern NJ
    I think you've got room for a couple more parts in there :)

    Tighter than the Madison Fielding amp I'm playing with for sure. I was thinking of doing something similar with a socket for bias testing on that, but using the goofy 4 pin phono power socket. Unfortunately I can't get both meter leads in there at one time, so that idea is out.
     
  3. primosounds

    primosounds AK Subscriber Subscriber

    Messages:
    1,363
    Not as tightly stuffed as the Sansui AU70 i am rebuilding now. This amp is has way too many features. But getting back to your build. Having so many trannys all together can result in unwanted interactions. I have also observed this, from afar of course, at the "he/she" bar in the red light district.
     
    drtool likes this.
  4. ferninando

    ferninando AK Subscriber Subscriber

    Messages:
    12,486
    Location:
    San Jose Ca.
    I managed to kram all this under mine
     

    Attached Files:

  5. battradio

    battradio Electron trainer Subscriber

    Messages:
    5,513
    Location:
    Near ST. Louis MO
    Had this up and running yesterday , had barely perceptible hum that rerouting one wire took care of . Been playing it a couple of hours now and it just keeps getting better . was going to do square wave tests and my generator decided it won't do square waves today .

    The power supply is dead quiet with the two chokes and the B+ is right at 265 volts . I used the second filament winding on the 6CA4 instead of the of dropping the B+ and tuned the power supply with the second choke to get the correct B+ .
     
    Leland47 and Retrovert like this.
  6. battradio

    battradio Electron trainer Subscriber

    Messages:
    5,513
    Location:
    Near ST. Louis MO
    It is on the way back to NJ ,
     
  7. ferninando

    ferninando AK Subscriber Subscriber

    Messages:
    12,486
    Location:
    San Jose Ca.
    what is purpose of 2nd choke in front?
     
  8. battradio

    battradio Electron trainer Subscriber

    Messages:
    5,513
    Location:
    Near ST. Louis MO
    I used the second filament winding to power the 6CA4 and used the second coke to lower the B+ to 265 volts using 4 UF as the first cap after the 6CA4 it also has less ripple than a one choke power supply
     
    Pio1980 likes this.
  9. ferninando

    ferninando AK Subscriber Subscriber

    Messages:
    12,486
    Location:
    San Jose Ca.
    I forget, but did DG mention that in his explanation?
    Sounds like a useful thing to do>
     
  10. battradio

    battradio Electron trainer Subscriber

    Messages:
    5,513
    Location:
    Near ST. Louis MO
    No that is something i do a lot using Duncan PSU designer II , will start out with a 1 uf cap and increase it till the voltage is exactly where it needs to be , using two chokes is much cheaper than buying the correct transfomer or using resistor that generates heat ..

    I also put a Kodak darkroom thermometer , i latched onto several years ago on the power transformer and it stayed right at 105 F , which is just fine because most transfomers are rated 160 F .The average human hand feels a burning sensation at 103 F .
     
    Pio1980 likes this.
  11. ferninando

    ferninando AK Subscriber Subscriber

    Messages:
    12,486
    Location:
    San Jose Ca.
    Thanks for the info
     
  12. vinyldavid

    vinyldavid Proud Jaguar Owner! Subscriber

    Messages:
    16,695
    Location:
    St. Louis
    Great work, Mark!
     
  13. Tim 700

    Tim 700 Active Member

    Messages:
    351
    I am the lucky owner of this vintage Magnavox 8601-20 I've bought a couple of consoles through the years at Estate Sales and have put their tube amps up on E-bay to generate cash to help fund my audio addiction. One Maggie I traded for a set of Infinity Renaissance speakers. Needless to say, I've missed having a vintage tube amp around for awhile, so when I was driving my daughter to school recently, this console on the curb caught my eye. I was hesitant to grab it because I had a busy morning, but dropped her off, went home and got a flashlight and a screw driver. With the garbage truck only 5 houses away, I peered into the ventilation holes and saw tubes! I put this rescue into my vehicle with only seconds to spare, it was almost lost forever. I immediately went home and pulled the amplifier section, checked out the model number and did some research. After finding out it was a bit on the rare side, being an SET amp, I was ready to bring this gem into the modern world. Thanks to the magic that is Audio Karma, I came into contact with "battradio" and he offered to do the modifications. With excellent communication, sound advise, more than reasonable rates and a quick turn around, this amp is now filling my living room with wonderful tube warmth. I'm blown away by the large sound stage and 3-D imaging. I just received the amp yesterday and have only streamed from my phone into a cheap Chinese tube pre-amp > NHT Super Zeros. I'm waiting for delivery of a Grant Tube Dac-11 which will play a vital role in this new system. The highs are clear and vocals are smooth. I've been streaming www.radioparadise.com which plays a large variety of music and I must say, I'm really impressed. Bass isn't everything I'd like, but I've hooked it up to an extra sub-woofer I've got laying around and this has solved that issue. I'm still at the beginning stages of experimenting and building a system around this amp and having a lot of fun doing it. I highly recommend grabbing one of these amps if you come across one and if you need any tube work done, Battradio is your man! I can't thank
    him enough for the top notch work he has done.

    upload_2017-10-11_15-36-47.png
     
    drtool, ldatlof and CopperWizard like this.
  14. battradio

    battradio Electron trainer Subscriber

    Messages:
    5,513
    Location:
    Near ST. Louis MO
    I have been taking in some simple projects from other AKers to get my hand eye coordination back , so i can finish a some other more complicated things that i owe others here that are long over do .

    The Imaging is from the way i star ground , and get the power supply as quiet as possible .
     
  15. Wharfcreek

    Wharfcreek AK Subscriber Subscriber

    Messages:
    3,696
    Location:
    Baltimore, MD
    Mark, I too offer my compliments! For the record, I've not had ANY PS related 'hum' problems with my builds of this amp when using only one choke. In fact, I did one with no choke at all and it was still dead quiet!! Not sure if that's 'typical'.....but seems to be consistent.

    Anyway......fun amps......great projects, good 'learning platforms'.....and certainly rewarding results. Welcome to the club!!

    Tom
     
    Tim 700 and ldatlof like this.

Share This Page