Fixing Ampex 354 - UK Vintage Radio Repair and Restoration Discussion Forum

mrmagnetophon · 20th Jan 2011, 9:29 pm

I have a schematic for my Ampex 354, although I'm trying to figure it out, it says db in reference to .78 volts for the VTVM, so can I just ignore that number and calibrate the VTVM like normal and use it to find the db? or do I have to calibrate .78 on the VTVM, 15 volts is 0 db on the VTVM though?

mrmagnetophon · 25th Jan 2011, 9:18 pm

Got that part figured out, but im trying to figure out why no sound comes out of my ampex 354.

EMI BTR 3 · 27th Jan 2011, 6:24 am

Have you got the manual and not just the schematics? The manual is very comprehensive with regards to troubleshooting (as an owner of a mega-modified 354 myself, I can attest to this).

Please give more detailed information as to how you have the machine connected and the controls set, what's plugged into the pair of sockets on the chassis near the input jacks, etc.

Jeff West · 10th Feb 2012, 9:32 am

I have been looking for an ampex 354 manual with no results

mrmagnetophon · 10th Feb 2012, 7:55 pm

I've got a binder with the manual and schematics. PM me I can print one for cost if you would like.

-Chris

mrmagnetophon · 20th May 2012, 6:07 am

OK so I'm back to work on this machine, completely recapped it and now when I turned it up real slow using the variac I heard a pop, which was from a spark of some sort.
When I first tried the machine out many years ago I had a spark across one of the cap solder joints on the board, I think its probably the same spot now.

What should I do?

And is it safe to just turn it back on and let it go for awhile to check things out?

I'm trying to figure it out but I've replaced just about everything now and it's getting so costly.

Chris

mrmagnetophon · 22nd May 2012, 5:24 am

After letting it spark and doing some more testing, I isolated the problem is in the left side, either bias oscillator portions or microphone preamp portions.
-Chris

mrmagnetophon · 23rd May 2012, 6:00 am

Well it looks like I have cured most of the faults, or maybe all.
Now I have to plug it into a amplifier, problem is my speakers are RCA unbalanced, and the ampex is balanced. Can I make a balanced to unbalanced cable, for the outputs?
In most cases it's fine to do so, but with valve equipment I am not sure.

Or is it better to run the xlr into the mic input on my mixer?

-Chris

TIMTAPE · 23rd May 2012, 7:28 am

Depends on what load it is supposed to look at.

You'd need to reduce the gain on your mic preamp so it's happy with a line level input. Usually you turn the channel strip trim control fully anticlockwise and if there's a further 20db attenuation switch, engage that too. Generally a line level signal is 50 to 60db bigger than a mic level signal. That's about 1000times.

EMI BTR 3 · 25th May 2012, 12:18 am

There are TRS headphone output jacks on the 354 electronics which come from the cathode followers pre-output transformers. The left jack is wired in the standard configuration, tip left channel, ring right channel; the right jack is the reverse, tip right, ring left, thus accomodating very early stereo phones with two separate TS plugs.

mrmagnetophon · 25th May 2012, 6:03 am

Right, I've got it playing back, haven't tested recording yet.
-Chris

GloryMorris · 13th Jul 2012, 12:34 am

I've been looking for 354 Schematics desperately for about a month. I have a client that dropped one off asking that I restore it. Can I get a copy as well?

20th Jan 2011, 9:29 pm	#1
mrmagnetophon Retired Dormant Member Join Date: Sep 2010 Location: Ohio, USA. Posts: 757	Fixing Ampex 354 I have a schematic for my Ampex 354, although I'm trying to figure it out, it says db in reference to .78 volts for the VTVM, so can I just ignore that number and calibrate the VTVM like normal and use it to find the db? or do I have to calibrate .78 on the VTVM, 15 volts is 0 db on the VTVM though?

25th Jan 2011, 9:18 pm	#2
mrmagnetophon Retired Dormant Member Join Date: Sep 2010 Location: Ohio, USA. Posts: 757	Re: Fixing ampex 354 Got that part figured out, but im trying to figure out why no sound comes out of my ampex 354.

27th Jan 2011, 6:24 am	#3
EMI BTR 3 Tetrode Join Date: May 2010 Location: Mountain Home, Arkansas, USA. Posts: 68	Re: Fixing ampex 354 Have you got the manual and not just the schematics? The manual is very comprehensive with regards to troubleshooting (as an owner of a mega-modified 354 myself, I can attest to this). Please give more detailed information as to how you have the machine connected and the controls set, what's plugged into the pair of sockets on the chassis near the input jacks, etc.

10th Feb 2012, 9:32 am	#4
Jeff West Retired Dormant Member Join Date: Feb 2012 Location: Hermitage, TN, USA. Posts: 2	Re: Fixing ampex 354 I have been looking for an ampex 354 manual with no results

10th Feb 2012, 7:55 pm	#5
mrmagnetophon Retired Dormant Member Join Date: Sep 2010 Location: Ohio, USA. Posts: 757	Re: Fixing ampex 354 I've got a binder with the manual and schematics. PM me I can print one for cost if you would like. -Chris

20th May 2012, 6:07 am	#6
mrmagnetophon Retired Dormant Member Join Date: Sep 2010 Location: Ohio, USA. Posts: 757	Re: Fixing ampex 354 OK so I'm back to work on this machine, completely recapped it and now when I turned it up real slow using the variac I heard a pop, which was from a spark of some sort. When I first tried the machine out many years ago I had a spark across one of the cap solder joints on the board, I think its probably the same spot now. What should I do? And is it safe to just turn it back on and let it go for awhile to check things out? I'm trying to figure it out but I've replaced just about everything now and it's getting so costly. Chris

22nd May 2012, 5:24 am	#7
mrmagnetophon Retired Dormant Member Join Date: Sep 2010 Location: Ohio, USA. Posts: 757	Re: Fixing ampex 354 After letting it spark and doing some more testing, I isolated the problem is in the left side, either bias oscillator portions or microphone preamp portions. -Chris

23rd May 2012, 6:00 am	#8
mrmagnetophon Retired Dormant Member Join Date: Sep 2010 Location: Ohio, USA. Posts: 757	Re: Fixing ampex 354 Well it looks like I have cured most of the faults, or maybe all. Now I have to plug it into a amplifier, problem is my speakers are RCA unbalanced, and the ampex is balanced. Can I make a balanced to unbalanced cable, for the outputs? In most cases it's fine to do so, but with valve equipment I am not sure. Or is it better to run the xlr into the mic input on my mixer? -Chris Last edited by mrmagnetophon; 23rd May 2012 at 6:28 am.

23rd May 2012, 7:28 am	#9
TIMTAPE Octode Join Date: Jul 2006 Location: Perth, Western Australia Posts: 1,971	Re: Fixing ampex 354 Depends on what load it is supposed to look at. You'd need to reduce the gain on your mic preamp so it's happy with a line level input. Usually you turn the channel strip trim control fully anticlockwise and if there's a further 20db attenuation switch, engage that too. Generally a line level signal is 50 to 60db bigger than a mic level signal. That's about 1000times.

25th May 2012, 12:18 am	#10
EMI BTR 3 Tetrode Join Date: May 2010 Location: Mountain Home, Arkansas, USA. Posts: 68	Re: Fixing ampex 354 There are TRS headphone output jacks on the 354 electronics which come from the cathode followers pre-output transformers. The left jack is wired in the standard configuration, tip left channel, ring right channel; the right jack is the reverse, tip right, ring left, thus accomodating very early stereo phones with two separate TS plugs.

25th May 2012, 6:03 am	#11
mrmagnetophon Retired Dormant Member Join Date: Sep 2010 Location: Ohio, USA. Posts: 757	Re: Fixing ampex 354 Right, I've got it playing back, haven't tested recording yet. -Chris

13th Jul 2012, 12:34 am	#12
GloryMorris Retired Dormant Member Join Date: Jul 2012 Location: Austin, Tx, US Posts: 1	Re: Fixing ampex 354 I've been looking for 354 Schematics desperately for about a month. I have a client that dropped one off asking that I restore it. Can I get a copy as well?