100K RN70D Mepco resistors on eBay right now

[sonicmojo]

I just thought I would point out to any 2nd/3rd gen enthusiasts that several lots of these rare blue resistors are listed on eBay right now. I snagged some but they may not last too long.

[ToneMerc]

Hate to bust your bubble, but actually those aren't the ones that are in Dumbles. When Phillips took over Mepco in 1971 they just rebranded Mepco/Electra using existing Phillips/Corning stock, eventually phasing out ME completely in 1986. All the "very light greenish blue" resistors that you see in Dumbles are definitely Electra.

These darker round cap blue resistors are Mepco/Electra from the early 70's most likely. They are still using the MF7C part number. When a company acquires another company's part numbers they usually phase them out quickly over just a few years. The MF7C number was probably gone by the mid-70s

Here's the actual Electra type used in early Dumbles. You see these exact ones in 2nd & 3rd Gen and also on the plates of the OD Deluxe.

https://tubeamparchive.com/viewtopic.ph ... sc&start=0

TM

[sonicmojo]

Ahh. Well at least they look nice. The first few I tested were dead on the money at least. This is probably as close as I'm probably going to get these days not having a stockpile.

[ToneMerc]

They are close because they are 1%. If I get a chance I will post some pics of the different types. You want to look for the ones that are very light blue and have the high gloss finish, these are also sans RN codes. The darker shades, almost sky blues and types with the RN designations including the matt finish are Phillips /Corning.

TM

[talbany]

Like These..

Tony

[ToneMerc]

Like These..

Tony

Tony, yes that the right shade and finish. Those are the bigger body and if they are like the few I have are marked as E RN70D. If you run across any, you want the ME MF7C (metal film precision) and MF6C, these have the pronounced endcap humps. These are what you will typically see in the Dumbles.

TM

[sonicmojo]

Like These..

Tony

Tony, yes that the right shade and finish. Those are the bigger body and if they are like the few I have are marked as E RN70D. If you run across any, you want the ME MF7C (metal film precision) and MF6C, these have the pronounced endcap humps. These are what you will typically see in the Dumbles.

TM

What are these RN65Ds? Assuming some of the same Corning since they say RN...

[ToneMerc]

Yes, they appear to be RN65. Also, I think they are some commonalities among different production runs as I found a few in my stash that are clearly early MF marked Electra's that look like Phillips only slightly lighter in color. FWIW, I'm pretty sure that if it says Electra it's the same core as the MFxC so I wouldn't sweat it. It's always cool to get exact period correct parts, but in this case the results will most likely be the same.

TM

[sonicmojo]

It's always cool to get exact period correct parts, but in this case the results will most likely be the same.
TM

I just wanted some blue ones. Be good to find red ones too, maybe green. So little color selection out there, really. Or maybe I've been watching my kids play video games too much where they sit for hours and just change the character costumes.

[diagrammatiks]

rn/rnc are just military designations.

each of the different brands had different colors for a while but since vishay bought almost everyone it's really just brown and more brown for new stuff.

but if you want red

IRC RN70d

[img:300:200]http://i.ebayimg.com/t/IRC-RN70D12-40K- ... Bt9G4C!EGk~$(KGrHqEOKkEEvNsEoVIIBL-TCMp5y!~~_35.JPG[/img]

green, blue, or whatever below.

I like the RLR32s which are a bright gentle shade of pastel blue.

33moons has a great id guide.

http://www.33audio.com/enter/606570.html

[passfan]

Just so I'm clear on what these are. If tonemerc has the time to look.. these are labled ME MF7C 1% 0 and the guy still has one lot for sale of 77 resistors. I already snagged a 100 so if anyone feels froggy, jump.
http://www.ebay.com/itm/77-LOT-VINTAGE- ... 27c0a5296f

[ToneMerc]

Passfan, I 've been doing some research over the last couple of days and enlisted the help of an authority on these resistors. We both had some questions as we had seen a few Electras with differnt markings and coatings. I updated my post above as well.

Here's the definitive answer after dissecting these exact ME 100K resistors.

Those Mepco-Electra are not the same construction on the inside as the Electra MF6C & MF7C. The Electra has a hexagonal end cap with silvering between the element and the cap. The M/E MF7C has a round end cap and no silvering. Only the copper end cap over the end of the resistive element. The elements appear to be the same. However, the Electra and M/E both have end caps which are copper.

The question is do these sound the same as the hexagonal end cap Electras found in the early Dumbles. In the picture below you can see the difference between the two, as those Electras have the hex end caps.

Hopefully this clears things up, as all the blue resistors on the 2nd/3rd Gen layouts should be marked as Electra.


TM

[passfan]

So the internal difference is the shape of the end caps, and silvering between the end cap and the element ? The elements are the same. I would almost bet you couldn't tell the difference given this information. Both being metal film it boils down to tolerance, and 1% is 1%. As long as they are within spec. Can you tell I'm not from the "critical" camp. I appreciate benefiting from your research. Thanks for taking the time to do it.
P.S.
Where are you finding your Mepco's these days?

[passfan]

Passfan, I 've been doing some research over the last couple of days and enlisted the help of an authority on these resistors. We both had some questions as we had seen a few Electras with differnt markings and coatings. I updated my post above as well.

Here's the definitive answer after dissecting these exact ME 100K resistors.

Those Mepco-Electra are not the same construction on the inside as the Electra MF6C & MF7C. The Electra has a hexagonal end cap with silvering between the element and the cap. The M/E MF7C has a round end cap and no silvering. Only the copper end cap over the end of the resistive element. The elements appear to be the same. However, the Electra and M/E both have end caps which are copper.

The question is do these sound the same as the hexagonal end cap Electras found in the early Dumbles. In the picture below you can see the difference between the two, as those Electras have the hex end caps.

Hopefully this clears things up, as all the blue resistors on the 2nd/3rd Gen layouts should be marked as Electra.


TM

Curiously, I see you using CDE's
coupling caps here, do you like the sound of those. I have a ton of these old pulls from organs but have yet to try them

[ToneMerc]

So the internal difference is the shape of the end caps, and silvering between the end cap and the element ? The elements are the same. I would almost bet you couldn't tell the difference given this information. Both being metal film it boils down to tolerance, and 1% is 1%. As long as they are within spec. Can you tell I'm not from the "critical" camp. I appreciate benefiting from your research. Thanks for taking the time to do it.
P.S.
Where are you finding your Mepco's these days?

Well it all depends who's magic mojo you believe; some folks say all the details are in the discrete endcap construction and materials even among metal films. I think there might be some truth to that because that is the transition point to the element. I've even seen talk that earlier resistors sound different because they were diamond wheel cut verses modern laser trimming.
In reality, how do you assign metrics and display tangible differences since so much of this stuff can be so subjective. I don't worry about it, I just try to use what was in the original target and it makes's for one less thing to to go I wonder if.............


I think these are the last from a batch that I found locally
I've also gotten a few values from 33Audio in the past as well. I think the 100K's that Mark has on his website now he got from eBay too. I reached out to him about the 100K's on his site and he was kind enough to dissect a few.

TM