The Fender Forum
NEW! LPF Facebook Page
NEW! LPF Instagram Page
Merchandise & Donations
NEW! Burst Serial Log Home Page
LPF Homesite
Results 1 to 7 of 7
  1. #1
    Les Paul Forum Member
    Join Date
    May 2019
    Posts
    15

    1959 Tweed Twin or Bassman Rich II MV Install tips

    I discovered an easy mod to make room to install a double 500K PEC Pot in a Tweed Twin or Bassman (or any 4-holer) by adding four flange nuts to to outside of the 7993 PT or the 8087 for the Bassman. In order to fit the dual pot in the ground switch location you need to move the PT housing out away from the chassis. The four flange nuts are the perfect thickness and make a clean reversible install. The 3rd screw on the slotted bracket will still fit in the slotted right angle PT bracket without mods. No need to enlarge the slot.

    When you remove the 4 nuts on the PT, pull the PT out enough to screw on the 4 flange nuts then place back into the amp chassis. I always put the serrated flange side of the nuts against the chassis. It just makes a secure bond connection as you see in the pics.

    This is a 1959 tweed Twin and I'm installing the Rich II master volume in this amp. I use special 3 wire silver tinned shielded wire to install this master volume, it's a 2 wire feed that is a clean install with a grounded shielded sheath in the wire. Makes a quiet no-issue MV install. I router the 3 wire feed under the circuit board and run the wires up from the bottom through the eyelets. After they get soldered snip-off the extra wire sticking up flush with the solder joint. When the shielded wires are routed under the board it's a cleaner install and less chance for interference.

    The cool thing is the small washer that comes with the PEC Dual 500K Pot has a washer that fits perfect inside the ground switch hole location. I use 3 of the internal pot washers to fit the pot properly. 2 Internal washers will work, 3 seems better.

    The chrome finish washer on the top finish side came from a Strap Lock hardware purchase. Makes a great finish washer.

    I use a Marshall Volume knob for the Master Volume on the Tweed Twin because it's small and round with a good line marker.

    Both the tweed Bassman and tweed Twin used the same circuit board and the screw that holds the board to the chassis is right between the two 220K bias resistors for the dual Tag board to use as a stand-off for the two .02 tone caps.

    I like this NV vs. the Lar Mar because you do not need to remove the two 220k bias resistors.

    And the Rich II MV sounds really good.

    For those who do not know this, Fender used LIN Linear Vol Pots in the Tweed Twin, Bassman, Pro, Super and Bandmaster tweed Amps. If you own any of these old amps you may want to look one day at your Vol pots to see what they are.

    On this mid 1959 Twin (dogbone handle) you can see in the one pic the Vol pots to the right. The round back Stackpole is an Analog LOG Vol Pot and to the right is a CTS Linear LIN Vol Pot. This Twin has one of each. They must have run out of the 1 Meg LIN Vol pots during production. My 1960 tweed Twin (JD) April 1960 has both Vol Pots with the 1 Meg LIN Vol pots. The 58 and 1957 Twin 5F8A amps have the 1 Meg LIN Vol Pots as well. I just wanted to point this out the next time you are under the hood.

    The Linear Vol pots have a wide sweep and work well when you jump the channels, back in the day the entire band would plug into the one amp, this may be why the R&D at Fender decided to use the LIN Vol pots on the larger amps.

    Jim Marshall told me he copied the schematic when he made the first Marshalls. The Fender schematics showed the amps used the 1 Meg Analog Vol Pots on paper, but not one amp left the factory with 2 Analog Vol pots. If anyone finds any of these old tweeds with both 1 Meg Analog Vol pots in the amp, please tell us what model and month-year the amp is. I always wondered if jim reverse-engineered the tweed Bassman would he have used the 1 Meg LIN Vol pots like the original fenders shipped with.

    This 1959 Twin is in good condition, has all the original components, I will show you a progress report when the Master vol is finished and the amp is all together. I have a set of Celestion Golds for this one. I had to make a new Baltic baffle because the originals are thin warped plywood. The center where the 2 speakers meet is the weak point. Baltic is the best solution. Remove all the old staples and install the original cloth on the new black painted Baltic baffle. No more rattles or buzz.

    The German made Simichrome metal polish is the best to clean the chassis with, this polish will not remove any of the white lettering.
    Brasso and other toxic metal cleaners will harm the white lettering. The Simichrome is like a pink toothpaste and works very well to clean up the tweed chassis faceplate area.

    I use a variac and drop the voltage down to 110v-115v. and a powerstation combined with the Rich II MV and it really improves the tone on the vintage Twin amp. The big iron sounds great dimed with the 5881 old tung Sol tubes cooking and a 5751 3 mica in V1 and two Sylvania 7025 in V2 V3. The old Mullard GZ34 is a must.


    The photos are large, you may need to DL them to get the full views.




































  2. #2
    Les Paul Forum Member
    Join Date
    Jan 2010
    Posts
    79

    Re: 1959 Tweed Twin or Bassman Rich II MV Install tips

    Interesting Oatie. I'll be looking forward to more on this thread. I have a '58 Twin (A-00243).

    Not sure I really need a Master Volume, but it might be something to try.

  3. #3
    Les Paul Forum Member ampdan's Avatar
    Join Date
    Feb 2007
    Location
    Salem WI.
    Posts
    409

    Re: 1959 Tweed Twin or Bassman Rich II MV Install tips


    You may want to fix these sketchy solder joints while you're in there....
    Hmmmm....picture not showing up for me?

  4. #4
    Les Paul Forum Member
    Join Date
    May 2019
    Posts
    15

    Re: 1959 Tweed Twin or Bassman Rich II MV Install tips

    Thanks Dan,

    I put new Atom 8uF-450v. bias caps in the old Astron cap covers to look old school, I have not soldered anything yet because I'm installing a bias pot in there too. This amp was a mess, I'm going to make it fun again. I'm putting a .68/160v. mustard in V2 in this amp to try it out.

  5. #5
    Les Paul Forum Member
    Join Date
    Jun 2007
    Location
    England
    Posts
    332

    Re: 1959 Tweed Twin or Bassman Rich II MV Install tips

    Quote Originally Posted by Oatie View Post
    I'm putting a .68/160v. mustard in V2 in this amp to try it out.
    Not sure what you mean by "in V2" but if this is a coupling cap 160v will not be enough.

  6. #6
    Les Paul Forum Member
    Join Date
    May 2019
    Posts
    15

    Re: 1959 Tweed Twin or Bassman Rich II MV Install tips

    Paul,

    It's a .68/160v. mustard for the V2A bypass cap, it piggybacks to the 820 ohm resistor like a Super Lead Marshall.

    Here is a pic of one of my Jan 17, 1972 JMP50 amps with Super Lead Spec., you can see the larger looking .68 mustard
    going to pin 3 of V2.

    In 1972 Marshall installed some voltage cards for the traveling musician, the card near the power switches is loose and
    not glued to the chasis. You can remove the card by removing the 2 nuts on the voltage select strip, then remove the card.
    It's wedged in that spot. Over the years most Tech's removed this card and you seldom see a USA build 1972 Amp with this card still in the amp.
    People always ask about the card, this is why I mentioned it. I have a Euro built 1972 JMP50 built 3 days before this amp and it has the voltage select switch on the amp rear faceplate so no card was needed. The Euro JMP50 was a regular spec amp with the 47K NFB and no bypass cap in V2.

    The early Marshall amps sound like a million bucks, I love the 1972 JMP amps. The mustards are very high quality and the carbon film resistors. I noticed the mustards in the 1974-1975 JMP amps with the PCB have smaller sized mustards in them, the .1/400v and .02/400v you can see the caps are a little smaller in size. And the resistors look like 1/4 watt on the PCB amps vs. the 1/2 watt resistors on the handwired amps.


  7. #7
    Les Paul Forum Member
    Join Date
    Jun 2007
    Location
    England
    Posts
    332

    Re: 1959 Tweed Twin or Bassman Rich II MV Install tips

    Ah OK, obviously no problem to use it as a cathode bypass cap As I am sure you know, adding a cathode bypass cap to V2 will increase the gain of that stage and will significantly alter the character of the amp.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  


Scroll Down And Click On All Of Our Sponsors' Logos For Their Websites!






i