170DC Lost a Channel

[toddalin]

I was listening to Ambrosia on the Altec Big Red Supers last night. Ambrosia recorded at Momma Jo's Studio in North Hollywood on Altec Big Red Supers and this was my first exposure to them (~1974) when I laid down some synthesizer track for a friend. Ambrosia was in the studio just before us, and some of their equipment (e.g., Baldwin electric harpsichord) was still there.

I've listened to these cuts dozens of time, but could easily pick out things that I had never noticed before.

Then disaster! I wasn't listening loud, but heard a "brap" "brap" from the right auxiliary woofer like a blown out surround.

I turned the volume on that channel on the 170DC down and brought it back up and the speaker worked without the "brap." Then the channel went dead (meter didn't appear to move) and turning down its volume increased the volume to the other channel.

Hopefully no damage was done to the woofer (I'll have to get to it later) and the problem is in the amp. Luckily, there is a local gent who worked as a Marantz certified tech who now works out of his garage located local to me.

I keep hearing horror storys about these things going out, but hoped that wouldn't happen. I guess it is 45 years old.

 

[jd3rdcoast]

Sorry to hear about the 170DC taking a dive. Your tech should be able to repair w/o too much trouble. Mine has been very reliable over the years and I have been able to make repairs as needed. Not too complex with dual amp boards to compare L & R sides. Good luck.

 

[toddalin]

Actually, when I started to diagnose things today, it would seem that it is the 1180DC console and the preamp for the right channel goes out but can be brought back by raising the volume, but goes out again momentarly when the volume is lowered. Perhaps it is dirty?

 

[toddalin]

I made arrangements to take all three pieces in to be checked/serviced (1180DC and two 170DCs).

One of the 170DC amps (from an AK member) is mint and has been rebuilt, but the right lamp is much brighter than the left, and certainly brighter than the two lamps on the other 170DC. I would hate to find out that the wrong lamp had been installed and would melt the housing, even if it cost the $40 minimum just to find out.

Alternatively, any lamp suggestions here to save the $40 minimum for what is an already rebuilt amp?

Also, what should I ask for to ensure that each piece is working as well as possible or even upgrades? For example, the rebuilt 170DC now has Mundorf caps.

 

[jd3rdcoast]

Alternatively, any lamp suggestions here to save the $40 minimum for what is an already rebuilt amp?

Lamps should be 8V 200mA fuse lamps found in most Marantz units of that era. If you decide to check them just be very careful with the lamp housing. It is VERY brittle can break easily and the screws can break the housing when reinstalling. Do not cross thread or tighten too much. I have cool white LEG's in mine and looks nice and bright .

Also, what should I ask for to ensure that each piece is working as well as possible or even upgrades? For example, the rebuilt 170DC now has Mundorf caps.

Primarily just make sure the 170DC's are set to factory specs for DC & Bias and that they both are output the same levels of rated power @ apx. 87 Watts/Ch. I really couldn't speak to upgrades. Mine is fully recapped.

 

[toddalin]

The bottom amp looks right and both are the same. The top amp is much brighter on the right and somewhat dimmer on the left compared to the bottom unit. The top unit was reported as rebuilt. Maybe a lamp was damaged in shipping though he did a very good job.

Shows difference better:

 

[jd3rdcoast]

There are 2 lamps per meter so at least one is burnt out on Left side. Recommend replacing both or all four at same time.

 

[toddalin]

Today I am taking the 1180DC and two 170DCs in to the shop for whatever may be needed. One of the 170DCs (reported by the AK seller as rebuilt and pristene) has a lamp out and the lamps on other meter seem too bright. I would hate to think someone had installed the wrong lamps which would melt the housing.

The 170DC that I got from the recording studio, with the Altecs, has scratchy pots and the protection relay seems a bit slow to engage (with a bzzzt).

The 1180DC (reported by the AK seller as working properly) has a problem in the at the right channel comes and goes with the position of the volume knob or even shutting down/re-powering the unit. I think this created the "brap" "brap" I heard in the right channel.

Luckily, there is an ex-Marantz employee technician located near me who now works out of his home. There is a $40 minimum per piece (applied to the repairs), but I imagine that even replacing the lamps in the 170 could amount to that or more.

 

[jd3rdcoast]

Sounds like they are in good hands. Hopefully a good cleaning and lamps will resolve most of the issues. Definitely want the protection circuits working properly, sounds like they are pushed hard with those speakers. Best not to have them clipping on a regular basis so watch the meters as well as the peak lights. I would think not a good idea to have them lighting up as part of normal listening. If they are, may want to consider amps with more than 87 WPC/RMS. Discuss your amp/speaker configuration with the tech and get his input.

Curious how you are configuring the 1180DC Pre-Out to each 170DC to the speakers?

 

[toddalin]

Sounds like they are in good hands. Hopefully a good cleaning and lamps will resolve most of the issues. Definitely want the protection circuits working properly, sounds like they are pushed hard with those speakers. Best not to have them clipping on a regular basis so watch the meters as well as the peak lights. I would think not a good idea to have them lighting up as part of normal listening. If they are, may want to consider amps with more than 87 WPC/RMS. Discuss your amp/speaker configuration with the tech and get his input.

Curious how you are configuring the 1180DC Pre-Out to each 170DC to the speakers?

Thanks,

These are pushing Super Reds in >15 cu ft (ext volume) cabinets which are probably among the most efficient speakers ever produced for the studio. I was watching and the meters never exceeded 20 watts during the peaks, and that would be into an 8 ohm load. These are 16 ohms, so the power use is roughly half of that.

1180DC pre-out ---> electronic crossover ---> 1180DC power amp in for horn, 170DC power amp for 604E2 woofer, 170DC for aux woofer.

 

[jd3rdcoast]

Thanks for that. I'm a novice in regards to bi-amping speakers. Always trying to learn. I should probably review some of the posts in Speakers forum on the subject. My 3250B PreAmp has PreOut 1 & PreOut 2 and could never find any information on how to utilize that feature. Op Manual was no help and could not find anyone who had utilized that feature. Currently using a single 170DC into set of HD88's.

 

[toddalin]

Interesting. When I took the three pieces into the shop today the two 170DCs from other sides of the country, had relatively close serial numbers. For some reason, the 1180DC NEVER RECEIVED A FACTORY SERIAL NUMBER! I wonder if this one went out the back door.

 

[toddalin]

I received a call today with the estimate. The tech actually had to do some of the repairs to see what needed further testing/repair.

The 170DC that I purchased from an AK member, billed as "recapped and in perfect condition"..., was not. Repair is ~$200.

The 1180DC that I purchased from an AK member, billed as "tried out and everything works properly"..., was not. Repair is >$200

The 170DC that I obtained from the studio with the Altec Super Big Reds also had problems. When it would start up, you could hear the relay "Bzzzt," rather than "click" and this required repairs. >$200

Total is $645. If it is of interest, I can post the work details when the repairs are completed.

 

[toddalin]

OK, I picked up the equipment today. Pretty general in the descriptions.

The Marantz 170DC amplifier that I bought from the recording studio:
Repair power supply to relay board assembly (relay was not engaging properly)
LEDs (replace lamps)
Clean all controls
Run, test, and set
(Parts not listed)
$185

The Marantz 170DC that I bought from an AK Forum member listed as rebuilt and in mint condition:
Repair left meter lighting circuit
Repair left meter
LEDs (replace lamps)
Clean all controls
Run, test, and set
4 LEDs
2 caps
$210

The Marantz 1180DC that I bought from an AK Forum member listed as in proper working order:
Replace defective pot, clean all controls and switches
Repair cold solder joints
Run, test and set
2 transistors
4 resistors
4 caps
$250

 

[Oerets]

I have those units and if need be would pay someone to them get the fixed too!