Metropoulos Forum

Does anyone have an opinion on trying to use NOS carbon film resistors. I am planning on using the .5 w Allen Bradley carbon comp resistors in the areas designated in the 50w Metro kit manual. Just curious about using NOS 1w carbon film in the other spots or is it just a waste of time?

Thanks
Kevrockitt

They'll be fine. I use all 1W carbon film in most of my builds. I'm not sure what your concern is regarding it being a waste of time.

Pihers are awesome but very hard to find a full set, and WILL cost you a fortune. Best try to avoid this sickness unless there is money to spare.

I experimented with Allen Bradley's and liked them at first. They added a little warmth to the tone. They added hiss too though. However, after about 6 months the amp started losing it's dynamic punch and just sounded lifeless. I put carbon films back in most spots and the amp came back to life and sounded much better. Some of them probably drifted high in value. I didn't test them. I currently only have CC's in the slope and NFB.

From what I've read, the main areas that might benefit from CC's are V2 cathodes, tone stack slope and NFB. I would NOT use them for inputs, mixers or plates because of the added noise. In general, I think they're more trouble than they're worth.

iskras and pihers have a subtle effect on sound. they sound a little more distorted than the 1w CF resistors george uses. the iskras sound real good for overdriven sounds. the pihers sound perhaps a tad more like CCs

Thank you guys for all the info. It really helps.
I do have another question... I have two NOS 8 pin McMurdo octal sockets for use in my build. The pin terminals on the underside are all slightly bent over. Should I leave them this way? I believe that they will fall through the actual pin hole if I straighten them out.
Any thoughts?

Does anybody know the time line on CC, CF resistors. I know they used CC early on, up till '63 maybe. Then came the Piher and the Iskras came in around late '67 in think. Hard to tell from all the pictures out there. I've seen some chassis that look all original that have CC and CF. Just would like to be as period correct as possible.

Thanks

around mid 67 you'll see more iskras and fewer pihers. CC are still used occasionally, esp. when long legs are needed

Iskras first appeared approximately late '66. Very often the late 66 and early '67 amps have either all Iskras or all Pihers. The all-Piher boards were typically solid, whereas the Iskra boards were perforated...just something I've observed. That doesn't mean that there aren't deviations from this, but it looks like they were put together on an assembly line, so you'd have batches which shared features. Iskras and Pihers coexisted through '67, but by the end of the year they'd gone to Iskras exclusively, with just the odd Piher and CC used, probably when a certain Iskra value was in short supply. I can't remember when they started using Pihers again, but sometime in the early 70s I think.

shakti wrote:Iskras first appeared approximately late '66. Very often the late 66 and early '67 amps have either all Iskras or all Pihers. The all-Piher boards were typically solid, whereas the Iskra boards were perforated...just something I've observed. That doesn't mean that there aren't deviations from this, but it looks like they were put together on an assembly line, so you'd have batches which shared features. Iskras and Pihers coexisted through '67, but by the end of the year they'd gone to Iskras exclusively, with just the odd Piher and CC used, probably when a certain Iskra value was in short supply. I can't remember when they started using Pihers again, but sometime in the early 70s I think.

Yes you see Pihers reappearing consistently in '71 with more Pihers relative to Iskras as the 70s went on.

Only the prototype JTM45s had carbon comps in large amounts, later amps still often used them on the V2 socket and for the cathode of V2a and feed to the tone stack, I they also seem to have used ccs on 67 and 68 amps in the bias circuit too.

One type we have not mentioned are the RS Hystab type which are colloquially known as the bumblebee resistors, they are fatter and rounder and browner than the usual red pihers. These were used on the prototypes and early coffin and block logo JTM45s.