Ampex 351-2 restoration project
Comments
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Let me make sure I'm correct. The previously measured 0.7 volt drop was actually across a 2.54 ohm resistor not a 1.5 ohm resistor, correct?
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I measured the 12.87 VDC with the power supply connected to the circuit so I don't think it would drop -- but let me know if I am missing something.
thanks! -
A few posts ago you measured a DC voltage drop of 0.7 volts on either side of 3R-60 that you assumed was 1.5 ohms. But once you pulled 3R-60 from the board you measured at as 2.54 ohms meaning that the actual voltage reduction was across a 2.54 ohm resistor instead of an assumed 1.5 ohm resistor. That means a different amount of current is flowing through the circuit.
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Yes, Ken, your previous statement is correct. Should I again measure the current flowing through the circuit? BTW: this is all with the original power supply board in-circuit. I have yet to install the new power supply board...so I am wondering if other components on the original power supply board were also out of spec(?).
thank you both! -
Yes, now that you know the actual value of 3R-60 put it back in the circuit, turn it on and let it stabilize for a few minutes and place your DC meter on each of the resistor's leads. Measuring what the voltage drop is across the resistor. Then take that voltage and divide it by the resistor's value. Now we will know the amount of current flowing in that circuit.
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Thanks Ken I will do so, and report back!
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Hello!
I recently acquired a 351-2 and although it is in decent shape, it needs some recapping. I just opened up the bottom of the motor/transport section and saw the motor caps are leaking everywhere.... I was going to go ahead and order new caps across the board, but am having trouble finding these motor caps. any leads?
Adrian in Richmond, VA -
Hello Adrian,
Be careful of any leaked material from those capacitors, try to dispose of it carefully. The supply and take-up values are 3.75uF and the capstan motor is 5.0uF with a voltage rating of 375VAC or higher. Several years ago I found them at Grainger.com
I hope this is helpful. -
Hi Ken:
Had the chance to sit down with this today... First I measured 3R60 out of circuit. It measured 2.1 ohms (I'm not sure why it would measure different from last time. I used the same meter and also checked it on a second meter). The voltage drop across 3R60 was 0.8 volts. So current flowing through the circuit is 0.38 A, correct? Please let me know what you think.
These measurements were all made with the old power supply, which I plan to replace with the new PCB I constructed.
thanks for your insight!
Steve -
Hi Steve,
The original goal was to drop the voltage by an additional 0.6 volts, giving a filament supply of 12.6 volts. The voltage drop goal would then be 1.4 volts, so 1.4 divided by 0.38 ampere gives a resistance of 3.68 ohms.
It looks like Digikey has a 3.5 ohm 10 watt, mil-spec resistor in stock with a part number of: MRA12-3.5ND for around $5.00 that would work. -
Thanks Ken, much appreciated!
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Good luck with everything!
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I will of course, keep you posted!
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The power supply is complete! (the rectifier tube is not in place in this photo)
Next step is removing the old PS board and installing the new one. -
Success! The power supply is installed and the unit is operating properly. Filament supply is 12.5 volts, which I think is pretty darn close. Here's a photo
Next I'll decide how to proceed with the record and playback cards. I think I'll rework the original cards instead of replacing them with new ones. Also just ordered a piece of perforated sheet metal so I can fabricated the missing "cage" cover for the top. -
Very well done, looks great!
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Thanks Ken!
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No problem, what's next?
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I just bought a perforated stainless steel sheet to make a 'cage' cover for the missing one. I guess that's next. I'll also start making a list of what I need to rebuild the record and repro boards. I think I'd rather refurb the old circuit boards as opposed to replacing them with new ones. I'm hoping to work on this a little more regularly in the coming weeks.
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Here are photos of the sheet, prior to any cutting. It's 20 gauge stainless. Not sure how I'll go about cutting this... I may use a Dremel tool.
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Hi Ken:
I hope you are well.
I've been re-working the record card and I'm almost finished. The last thing I need to do is install the multi-section capacitor, C2. I'm replacing the multisection cap with individual caps, and I believe that I have nailed down the position of each of the new cap based on the legend on the old cap.
One of the solder pads for the old multi-section capacitor has no electrical connection to the rest of the circuit board. It looks like the pad was there for mechanical purposes. This particular pad was for one of the can case legs. On the can case it says ""CAN COM NEG").
If I understand correctly, the three can legs are common and negative. I believe that I need to tie that one isolated solder pad to one of the other two in order to provide a negative connection for the new separate capacitor, or tie the negative lead of that cap to the negative lead of one of the other two new caps. Does that sound correct to you? Let me know if I did not explain clearly. Thanks, best
Steve
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Yes, you are correct. The original capacitor's case provided the negative side for all the sections.
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Thank you very much Ken, I appreciate the response.
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Looks like I have run into a speed bump. I finished reworking the record card and when I started to re-insall it, a few of connectors that attach to the PCB broke due to being brittle. I may have to reconsider replacing the original record and repro PCBs with replacements from GAS. :-(
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If you do a search on eBay for "Ampex 351" you should find a seller who has a bunch of the connectors with wire attached. I found some Fastons that came close to fitting the circuit board connections but still need to be adjusted with pliers, if you'd like some I can locate them?
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Thank you Ken, I'll do some snooping on Ebay and if I have trouble finding them I'll let you know.
Much appreciated! -
Hi Guys! It was a long busy summer (lotsa' work, which is always good I suppose...). Here is an update on the project. I decided to go with new Repro and Record PCBs from GAS. Here are some photos:
The new PCBs:
The Record PCB in progress:
Record PCB almost finished:
Record PCB installed:
More later!
peace
Steve -
Very nice, Steve! Did your unit have all those copper washers underneath the circuit board isolation suspension corners?
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Hi Ken, thanks.
Good question about the copper washers. They definitely were in place underneath the power supply board. Im going to double check the other two boards. I'm pretty sure they were in place when I installed the Repro and Record PCBs. I imagine that if they weren't, the PCBs would bottom out and short -- in which case I'd certainly know!
Thanks for the heads up. -
Hi Ken:
I double checked... the copper washers are all in place underneath the corners of the PCBs. More photos coming...
![[Deleted User]](https://w8.vanillicon.com/83b82048d67877ca27bbc25d5d38f9d3_100.png)
