Building an Ampex MR-70 playback preamp
Options
Comments
-
The company is called: JLCPB
-
Some additional nuvistors arrive, some 6CW4:
-
I prefer to use circuit board turrets for my connections, to my mind they allow for easy attachment and undoing of wires and I just plain like them. The smallest I could find of a good quality have a 1.6mm insertion base. Wanting to get a close tolerance fit I ordered, from McMaster-Carr, two drill bit sizes. The one on the left is 1.61mm and the one on the right is 1.65mm to see which one is better.
-
I ended up using the 1.61mm drill bit with the slightly less deep version of the turret. The goal is to have a nice even rolling of the bottom end of the turret after striking.
-
-
Is it just a mechanical connection to the traces (i.e., no solder)?SystemLuxman L-590AXII Integrated Amplifier|KEF Reference 1 Loudspeakers|PS Audio Directream Jr|Sansui TU-9900 Tuner|TEAC A-6100 RtR|Nakamichi RX-202 Cassette
-
After staking the turrets I do a continuity check between each terminal and the circuit board trace it's connected to. Then I solder the underside of the turret to the solder pad and repeat the continuity test. In fact I found a failure on one of the turret connections, so I'm scrapping that board and doing it over. That's why I had 10 boards made in case of a problem.
There are two methods of staking the turrets that I've used. One is to place the anvil part of the tool in a vise and then using the staking tool (a rod with a shaped point) and a hammer tap the tool until the turret is firmly seated. The other approach (which I prefer) is a different anvil support that is a threaded bolt and a collar to hold the anvil. The threaded bolt is placed in a drill press table and then the striking tool is installed in the chuck of the drill press. Then with everything aligned the drill press handle presses down on the turret and makes a perfect punch. Unfortunately a longtime ago I left the anvil I was using in the collar instead of taking it out. Now the anvil is stuck in the collar and I can't change it to the correct anvil for this sized turret. So, I've ordered another tool from Mouser and have learned a lesson.
With circuit boards this long holding the board while aligning the striker tool correctly over the turret and then hitting with just the right amount of force with a hammer is too unwieldy, I'll get the correct tool and do them properly this time. -
Here's a photo of the last 6CW4 nuvistors I need:
Post edited by SeleniumFalcon on -
A bundle of resistors needed for the main playback circuit boards:
-
The Keystone terminal staking kit 1721:
-
Found your wing nut, 😂😂
-
-
Do you set the down stop so you rivet the same amount each time, or do you "get the feel" for when to stop?Sources: Technics SL1200MKII | SME3009 Tonearm | Monster Alpha 1 MC cartridge | Oppo UDP203 disk player | Nikko NT-790 analog tuner | Musical Fidelity Trivista 21 DAC | Preamp: Threshold SL-10 | Amplifier: Threshold Stasis 2 | Speakers: Snell Acoustics C/V | Kimber 12-TC bi wire speakers | Analysis plus Oval 1 preamp to amp | Wireworld Eclipse 7 DAC to Preamp | Wireworld eclipse digital IC Oppo to DAC | Audioquest Quartz tuner to preamp |
-
Now that you mention it, I should have used the down stop. No, I can feel a bit of resistance then a compression squeeze and it's set. I use a magnifying visor so I can get a close look at what is happening and check for the tightness of the fit and then a continuity check after each board.
-
-
I've installed almost all of the resistors on both of the larger boards:
-
The larger value WIMA and EPCOS/TDK capacitors:
-
One of the goals in this project was to not use any electrolytic capacitors anywhere, including the power supply. I was able to find a 1,000uF and 2,000uF polypropylene capacitors. The Quaker Oats box is the large (42oz) size:
-
-
With the exception of a 0.5uF capacitor (I ordered the wrong part) the two larger circuits are complete. Now I have to finish the smaller, output stage, boards.
-
-
I actually looked in the pantry at a 42oz oat can and did a double-take.
Don't take experimental gene therapies from known eugenicists. -
-
I take it there's no Clarity Cap option.Don't take experimental gene therapies from known eugenicists.
-
-
I've finished the second pair of circuit boards that contain the output circuitry. This circuit connects with an output transformer to create the balanced outputs.
-
-
Now I'm working on the power supply, gathering all the parts. I ran into one difficulty, I ordered a 15mH choke from Digikey made by Signal Transformer, normally an excellent source of parts. When I got it the coil bobbin had been painted black but there were chips on several parts. I tested the value and it measured 11mH @ 1kHz instead of 15mH. So, I've begun a claim with Digikey.
-
-
