Marantz 7C / Consolette Restoration Strategy Questions
- Thread starter chinacave
- Start date
chinacave
Its Like a Jungle Sometimes; It makes me Wonder
SO its been a while and I am back with these.
After talking to the units' owner, he has decided to have me NOT do the 1981 POOGE update / mods, (complexity and he is VERY familiar with their sound - he owns and uses 3) but update the power supply 1st and then replace caps and resistors (if needed ) with reasonably available parts.
I would be curious to learn where one might buy the "AZ" Caps , formerly Westcaps... I was planning on using Solens for the coupling caps / or OD 716Ps for the tone controls......
Here is the formerly busted 7C on the bench. Serial # 19719
I DID get a couple special order tape monitor switches from Switchcraft, all is perfect except they could not make the flat shaft as long as the original ones - I am pondering ways to remedy that.
after REMOVING my ham-fisted 'correction' of the breaks in the ground buss, re-soldering the several caps that were lifted (!) and installing the new Tape monitor switch, I brought the unit up on a variac, watching current draw and voltage the whole time. I almost need not have bothered - like the other gear I have worked on for this gentleman, esp the 8B that I checked out (only had to replace one bad coupling cap - did the other 3 as well) - the voltages were nearly spot on -
At 120V AC Line - all the B+ voltages were within a few % of nominal (pix shows B+3 at R109/ C103C - listed as 245 - was 223-220, filament voltage listed as 18.9 - was 17.9 - I'd call that spot on for a 50 YO bit of gear.
New Tape switch from the inside;
Shows the slightly shorter shaft of the new tape monitor switch, at the top;
Section of the PS schematic - voltages observed in red -
I just got the new caps to re-stuff C102 and C101 (derated for voltage - ie calls for 350 V / I am using 400v [highest v. I could find in the stuff-able caps]) and am using a CE can cap for C103, again, derated for voltage (calls for 350 V - I am using 475v)
In noodling around the interwebs - looking to see what other folks have done in a similar situation, I found the following of interest
S Hoffman site / post #33 (middle of the page)
7C updated by Sid Smith
After talking to the units' owner, he has decided to have me NOT do the 1981 POOGE update / mods, (complexity and he is VERY familiar with their sound - he owns and uses 3) but update the power supply 1st and then replace caps and resistors (if needed ) with reasonably available parts.
I would be curious to learn where one might buy the "AZ" Caps , formerly Westcaps... I was planning on using Solens for the coupling caps / or OD 716Ps for the tone controls......
Here is the formerly busted 7C on the bench. Serial # 19719
I DID get a couple special order tape monitor switches from Switchcraft, all is perfect except they could not make the flat shaft as long as the original ones - I am pondering ways to remedy that.
after REMOVING my ham-fisted 'correction' of the breaks in the ground buss, re-soldering the several caps that were lifted (!) and installing the new Tape monitor switch, I brought the unit up on a variac, watching current draw and voltage the whole time. I almost need not have bothered - like the other gear I have worked on for this gentleman, esp the 8B that I checked out (only had to replace one bad coupling cap - did the other 3 as well) - the voltages were nearly spot on -
At 120V AC Line - all the B+ voltages were within a few % of nominal (pix shows B+3 at R109/ C103C - listed as 245 - was 223-220, filament voltage listed as 18.9 - was 17.9 - I'd call that spot on for a 50 YO bit of gear.
New Tape switch from the inside;
Shows the slightly shorter shaft of the new tape monitor switch, at the top;
Section of the PS schematic - voltages observed in red -
I just got the new caps to re-stuff C102 and C101 (derated for voltage - ie calls for 350 V / I am using 400v [highest v. I could find in the stuff-able caps]) and am using a CE can cap for C103, again, derated for voltage (calls for 350 V - I am using 475v)
In noodling around the interwebs - looking to see what other folks have done in a similar situation, I found the following of interest
S Hoffman site / post #33 (middle of the page)
7C updated by Sid Smith
Last edited:
chinacave
Its Like a Jungle Sometimes; It makes me Wonder
Back at the 7c's and a B+ voltage dropping Question
For anyone still interested - A question on dropping B+ voltage after installing a new modern diode is buried below -
Now there are three.
I finished the power supply on the first unit and the voltages fell right in line with the re-stuffed (2) and new (CES) can caps and new dropping resistors between them - I left the original selenium rectifiers for B+ and filament in place as they seem (? how to check the sel. rectifiers for sure?) fine.
Voltages as noted below. Also replaced all of the bumble-bee coupling caps and electrolytic bypass caps on the tube tagbord and two resistors that were out of spec. I used a mix of Solens, Russian K-40 oil caps and 716P 'orange drops'
As I am afraid of the tightly- packed caps on the tone controls, for now I am leaving them be. Several are cracked, but they sound fine to me (no drop-outs when switching through them,) and observing square waves through a scope while switching through each, I only saw the same tilting on the waves - no idea if that is a valid initial test, but they are out of the signal path when the controls are set flat - I will save attacking that for later -
I took the unit with the restored power supply and now new coupling caps to their owner to hook them up with two of the Mc-40's I re-built last year, and as he was heading south for the winter, he loaded a third 7C in my car to re-furbish with the two I already have... I was really looking forward to hearing them through his giant Tannoy co-axials... Later I guess.
For my efforts, he laid a Thorens TD-124 and SME arm on me, with a cartridge or two. Very generous gent. Has been for years. I have him to thank for the pair of B&W DM-70 hybrid electrostats that were in a Sterling Sound / NYC Mastering studio for years. The TD-124 is shortly off to Jim (? Campbell ) in PA. for a complete restoration -
So now I have all three 7c's on the bench, two for for new power supplies and check-out via my meager skills. One for reference. I need a bigger bench.
PS Schematic for reference - these are the voltages for #19719 a few months ago.
7C PS detail
The one unit I have 'finished with' is #19719 -
Nominal voltages on the PS below are first - observed ones are in bold.
My wall voltage is pretty steady at 120, but all these were tested at a measured 120v from the Variac so as to have a solid base reference.
#19719
After rectifier #1 (328) 331
B+1 (280) 284
B+2 (265) 266
B+3 (245) 248
Nice!
So I restored the power supply of the next one - Serial # 14604 -
This one has the original Selenium B+ rectifier and a replacement bridge for the filament voltages
Re-stuffed the PS caps C-101 & C-102 (Nichicon 105deg. C) and use a new CES EC 50x4-350 for C-103 (85 deg. C) with new resistors
Here is today's Question;
How to best drop the B+ voltage after installing a a new diode? The existing selenium one is putting out B+ too low, so I substituted-clipped in a UF4007, and it was WAY too high - like 400+ V. I tried clipping in first a 100K pot, then a 500K pot immediately after the diode, to see if I could arrive at a value R to get the initial target 328V in line, but no go. All efforts ended up too high. Almost as if the added resistance of the Pot was too low!
I did some reading and it seems the normal resistances added are on the order of 100+/- ohms, or a choke, or adjust the first capacitor. Most of the threads I read were dealing with power amps that draw significant current - this is 'only' a pre-amp. so very limited current needs.
With the resistor, the voltage at C102(a) came up much more slowly, though.
That was not working, so I re-installed the old selenium one and took some measurements:
After rectifier #1 (328) 296
B+1 (280) 253
B+2 (265) 237
B+3 (245) 220
Bummer. A bit low. Fil is on target at (18.9) 19.6 The other two as well - Filament withing spec, B+ low or REALLY low (See below)
Any Ideas? Suggestions?
To make my day complete, I took as-is voltages on the third unit, which Jerry and I removed from his living room system, working, where it had been for (I believe) several / many years)
Serial # 16123 - Original B+ rectifier #1, new/ old / repaired Bridge for the filament Rect. 2
After rectifier #1 (328) 91.9
B+1 (280) 80.6
B+2 (265) 74.8
B+3 (245) 68.2 WTF??!!!
And it played music and sounded fine..... I double and triple checked the test lead connections. The music did not fade out until the B+1 dropped to 33v!
This is something I have noticed with the 7C - it will keep playing FINE long after the power is cut off - I can't see how the power supply is any different (please let me know if it is) than other pre-amps I have seen - Scott 130, Dynaco Pas, Melos GK1, - all of them drop sound 2-5 seconds after the power is killed, this plays for 10-20 seconds.
All voltage tests were done while listening to Schubert playing through my shop amps - Heath UA-1 (rebuilt - still some slight troubleshooting to do..)
Oy.
For anyone still interested - A question on dropping B+ voltage after installing a new modern diode is buried below -
Now there are three.
I finished the power supply on the first unit and the voltages fell right in line with the re-stuffed (2) and new (CES) can caps and new dropping resistors between them - I left the original selenium rectifiers for B+ and filament in place as they seem (? how to check the sel. rectifiers for sure?) fine.
Voltages as noted below. Also replaced all of the bumble-bee coupling caps and electrolytic bypass caps on the tube tagbord and two resistors that were out of spec. I used a mix of Solens, Russian K-40 oil caps and 716P 'orange drops'
As I am afraid of the tightly- packed caps on the tone controls, for now I am leaving them be. Several are cracked, but they sound fine to me (no drop-outs when switching through them,) and observing square waves through a scope while switching through each, I only saw the same tilting on the waves - no idea if that is a valid initial test, but they are out of the signal path when the controls are set flat - I will save attacking that for later -
I took the unit with the restored power supply and now new coupling caps to their owner to hook them up with two of the Mc-40's I re-built last year, and as he was heading south for the winter, he loaded a third 7C in my car to re-furbish with the two I already have... I was really looking forward to hearing them through his giant Tannoy co-axials... Later I guess.
For my efforts, he laid a Thorens TD-124 and SME arm on me, with a cartridge or two. Very generous gent. Has been for years. I have him to thank for the pair of B&W DM-70 hybrid electrostats that were in a Sterling Sound / NYC Mastering studio for years. The TD-124 is shortly off to Jim (? Campbell ) in PA. for a complete restoration -
So now I have all three 7c's on the bench, two for for new power supplies and check-out via my meager skills. One for reference. I need a bigger bench.
PS Schematic for reference - these are the voltages for #19719 a few months ago.
7C PS detail
The one unit I have 'finished with' is #19719 -
Nominal voltages on the PS below are first - observed ones are in bold.
My wall voltage is pretty steady at 120, but all these were tested at a measured 120v from the Variac so as to have a solid base reference.
#19719
After rectifier #1 (328) 331
B+1 (280) 284
B+2 (265) 266
B+3 (245) 248
Nice!
So I restored the power supply of the next one - Serial # 14604 -
This one has the original Selenium B+ rectifier and a replacement bridge for the filament voltages
Re-stuffed the PS caps C-101 & C-102 (Nichicon 105deg. C) and use a new CES EC 50x4-350 for C-103 (85 deg. C) with new resistors
Here is today's Question;
How to best drop the B+ voltage after installing a a new diode? The existing selenium one is putting out B+ too low, so I substituted-clipped in a UF4007, and it was WAY too high - like 400+ V. I tried clipping in first a 100K pot, then a 500K pot immediately after the diode, to see if I could arrive at a value R to get the initial target 328V in line, but no go. All efforts ended up too high. Almost as if the added resistance of the Pot was too low!
I did some reading and it seems the normal resistances added are on the order of 100+/- ohms, or a choke, or adjust the first capacitor. Most of the threads I read were dealing with power amps that draw significant current - this is 'only' a pre-amp. so very limited current needs.
With the resistor, the voltage at C102(a) came up much more slowly, though.
That was not working, so I re-installed the old selenium one and took some measurements:
After rectifier #1 (328) 296
B+1 (280) 253
B+2 (265) 237
B+3 (245) 220
Bummer. A bit low. Fil is on target at (18.9) 19.6 The other two as well - Filament withing spec, B+ low or REALLY low (See below)
Any Ideas? Suggestions?
To make my day complete, I took as-is voltages on the third unit, which Jerry and I removed from his living room system, working, where it had been for (I believe) several / many years)
Serial # 16123 - Original B+ rectifier #1, new/ old / repaired Bridge for the filament Rect. 2
After rectifier #1 (328) 91.9
B+1 (280) 80.6
B+2 (265) 74.8
B+3 (245) 68.2 WTF??!!!
And it played music and sounded fine..... I double and triple checked the test lead connections. The music did not fade out until the B+1 dropped to 33v!
This is something I have noticed with the 7C - it will keep playing FINE long after the power is cut off - I can't see how the power supply is any different (please let me know if it is) than other pre-amps I have seen - Scott 130, Dynaco Pas, Melos GK1, - all of them drop sound 2-5 seconds after the power is killed, this plays for 10-20 seconds.
All voltage tests were done while listening to Schubert playing through my shop amps - Heath UA-1 (rebuilt - still some slight troubleshooting to do..)
Oy.
