I am recapping a Marantz Model 9. While I was in there I noticed some of carbon composition resistors have drifted over the years. Are there any resistors that must stay carbon composition for best performance? And any positions that would benefit from a specific type like wire wound? I plan on using thin/thick film resistors as long as they have the correct voltage rating and low ppm.
http://zilla.li/Resources/PDF/Marantz_8B_9/Marantz_9_Service_Manual.pdf
Thanks!
http://zilla.li/Resources/PDF/Marantz_8B_9/Marantz_9_Service_Manual.pdf
Thanks!
Use metal film resistors of the correct rating. Old CC resistors were what gave old tube equipment the reputation of being noisy and having lots of hiss. The metal film resistors are more stable and quieter.
Some folks feel that grid stoppers, like R41 etc., should be carbon comps. I use them in my amps because I have a large stash of 1K and 10K ones, but I'm not sure it's necessary. I happen to think they preserve a touch of the "old-fashioned" warmth, but I'll probably get some pushback on that. ;-)
Consider what you will do to its status as a classic tube timepiece if you mod it.
You can be rest assured that the value will go down as nobody wants a modified classic that they are interested in.
If you just have to diddle with it , try and make it look stock at all costs - quite literally
-Antique furniture should stay as it came.
Refinish it and there goes it value-
You can be rest assured that the value will go down as nobody wants a modified classic that they are interested in.
If you just have to diddle with it , try and make it look stock at all costs - quite literally
-Antique furniture should stay as it came.
Refinish it and there goes it value-
Yes, the grid stoppers benefit from non-inductive resistors and CC fit that position. The modern CC are better than the old ones were. It’s still ok to use MF there but traditionally it’s CC. Use the highest wattage units you can as they handle the voltage better. I use 1 watt everywhere as they are just a little more expensive than half watt ones. Don’t spend rediculous money on boutique parts as they are really not worth the price. Stuff like PRP for one watt or TKD for 2 watt resistors are plenty good. Most of the old Allen Bradley CC resistors are like 40 years old production and have aged just sitting around. The difference in noise will be dramatic with the new resistors and proper operation will be back. All the film caps should be ok but the power supply electrolytic caps might be bad. They dry out over time and no longer are to spec. New ones can be found but if you can find room under the chassis just put new electrolytics under the chassis ad move the wires or extend them. That keeps the look but updates the caps.
A week has a point but if it’s for you and you want to safely use it make the upgrades. If you’re going to sell it then don’t touch it.
I own the reissues from 1997. The carbon composition resistors are rated for +-5% however some measure as +-10% to +-20% with my Fluke. Two of the resistors measure worse at +-30%. So no matter what some carbon composition resistors are being replaced. The few metal films used by VAC measure right on spec.
I am having bias stability issues but that could be the capacitors as they are 30 years old. While I am in there I figured replacing the out of spec resistors would be a good idea. Bias drifts after 2-3 hours, then when I adjust the bias it drifts again after 2-3 hours more. Each Model 9's bias drifts just like the other, always up and down at the same rate and DC balance remains perfect. However, I doubt it's line voltage because it always drifts up then down at the same 2-3 hour mark after weeks of use.
Which value resistors are the grid stoppers in the service manual? Just the four 1K resistors like R41 that grovergardener mentioned?
I am having bias stability issues but that could be the capacitors as they are 30 years old. While I am in there I figured replacing the out of spec resistors would be a good idea. Bias drifts after 2-3 hours, then when I adjust the bias it drifts again after 2-3 hours more. Each Model 9's bias drifts just like the other, always up and down at the same rate and DC balance remains perfect. However, I doubt it's line voltage because it always drifts up then down at the same 2-3 hour mark after weeks of use.
Which value resistors are the grid stoppers in the service manual? Just the four 1K resistors like R41 that grovergardener mentioned?
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As for restore/not restore, if I were on the lookout for a vintage Marantz piece, I'd want one that is working properly and running to spec. IMO it does no service to the equipment itself to make it struggle against aging, out-of-spec components. 30 years ago, "original" classics were highly valued on the market. Now those pieces have had thirty more years to decay and either smoke at start-up or sound like they were bought at Radio Shack. What's the point in that?
That's what I was thinking. The power transformers run a bit hot but not enough to be concerned about yet, replacing the non-filter capacitors before it becomes a real concern. In-spec is better than out of spec with carbon comp. Peoples obsession with stock leads to burned out transformers and an in-spec amplifier will always sound better regardless of resistor type.
Mouser literally only has four choices for carbon composition resistors. And Digikey 156 choices in stock. I'll need to check later but I think the 1K resistors were right on spec. I watched a video on Youtube of a restoration and It's the other resistors not in the audio path that appear to have drifted in mine.
Mouser literally only has four choices for carbon composition resistors. And Digikey 156 choices in stock. I'll need to check later but I think the 1K resistors were right on spec. I watched a video on Youtube of a restoration and It's the other resistors not in the audio path that appear to have drifted in mine.
Amtrans make excellent modern carbon comp resistors in a vast range of values in 0.75 w and 2watt ratings. They also sound great.worth the effort.and you guessed it they are reassonably priced.
The Amtrans AMRG and AMRT are carbon film resistors, this type is easily available at Mouser however these seem to be made with audio in mind. I do see the AMRW range however those appear to be composite resistor wire wound. A compromise to bring the best of both worlds?
Is this half carbon composite or half carbon film? Also, what voltage rating should I be using for the resistors? I was looking at 500V to 700V on Mouser. These AMRW's seem to have a 400V max working voltage.
Looks like Carbon Film to me however I may be mistaken.
Is this half carbon composite or half carbon film? Also, what voltage rating should I be using for the resistors? I was looking at 500V to 700V on Mouser. These AMRW's seem to have a 400V max working voltage.
Looks like Carbon Film to me however I may be mistaken.
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Modern metal film resistors have super low inductance, basically the same as an inch of wire. The values under 10 ohms are slightly higher but only a few nH.
For audio applications metal film is superior in every way.
For audio applications metal film is superior in every way.
I own three Marantz Model 9 amplifiers. One of them, which had never been used and was still sporting its original tubes and completely dust-free interior, showed significantly drifted resistor values when I finally checked it. For instance, the 100-ohm resistor measured 130 ohms, and many other resistors had similarly gone off-spec. It seems like decades of storage allowed moisture to seep in, causing these changes.
On the other hand, I have another Model 9 that I’ve used continuously, which suffers from bias drift. Interestingly, all of its carbon composite resistors still measure within spec. This suggests that the issue might not be with the resistors themselves, but rather with aging capacitors or perhaps a need to replace certain critical resistors with more stable, low-ppm metal film types to achieve stable bias.
My two regularly used Model 9s both exhibit the same pattern of bias drift: they both drift up and down at the same rate, and the DC balance remains perfect. Around the third hour of operation, the bias tends to drift upwards; by the sixth hour, it drifts back down. This behavior repeats like clockwork, no matter what time of day I run the amps. Given how consistent and repeatable it is, I don’t believe line voltage fluctuations are the cause.
100V models each with their own 500W step down transformer.
On the other hand, I have another Model 9 that I’ve used continuously, which suffers from bias drift. Interestingly, all of its carbon composite resistors still measure within spec. This suggests that the issue might not be with the resistors themselves, but rather with aging capacitors or perhaps a need to replace certain critical resistors with more stable, low-ppm metal film types to achieve stable bias.
My two regularly used Model 9s both exhibit the same pattern of bias drift: they both drift up and down at the same rate, and the DC balance remains perfect. Around the third hour of operation, the bias tends to drift upwards; by the sixth hour, it drifts back down. This behavior repeats like clockwork, no matter what time of day I run the amps. Given how consistent and repeatable it is, I don’t believe line voltage fluctuations are the cause.
100V models each with their own 500W step down transformer.
If you are trying to preserve the original look while replacing out-of-spec carbon comp resistors you might want to look at Just Radios. They sell new production carbon comps in the original axial brown tubular form factor.
The Just Radios site can be a little difficult to navigate so here is a link to the resistor portion of the site.
Resistors for Tube Radios and Tube Electronics
Resistors for Tube Radios and Tube Electronics
Thanks. I'm going to try replacing the capacitors first, then I'll visit the resistors outside the signal path that affect bias stability if still unstable. Will report back after Christmas, takes time for the Mouser order to arrive and Xmas stuff.