soliciting input re: resistor brands for my first Marshall build

[zephyrblau]

I've been reading... and reading... and looking at pictures... and reading some more... here, Marshall Forum, Metro. it's becoming a blur.
the intent is to mimic an original amp from a tonal perspective as practicality allows.
so...
the victim is a JTM45, my first attempt at a Marshall. I may or may not have the caps sorted. more on that later. on to resistors;
ISKRA
PIHER
AB
I've seen amps with ISKRA across the board and others with a mix of ISKRA and PIHER. not sure I've seen any AB yet but some here like to include them in the mix. possibly for reasons of economy (?)
given that I'm a paint-by-numbers guy and am not up to speed with terminology I'll list the values from the Metro assembly guide.
please list your favorite brand for each / any value.

1 WATT CARBON FILM RESISTOR
1 470 OHM
2 820 OHM
1 1K
4 1.5K
1 2.7K
4 5.6K
1 10K
1 15K
1 27K
1 33K
1 47K
1 56K
5 68K
1 82K
4 100K
1 150K
3 220K
2 270K
3 470K
4 1M

I have a few ISKRAs on hand (33K, 68K 470K IIRC) and more than that on the Piher front.
there won't be a problem acquiring any Abs I don't already have.
input appreciated.
TIA
jerry

[Reeltarded]

Well, the resistors changed (brand) only when out of stock in any given period. Pihers for JTM45 are expected. Iskras are later. Nothing wrong with mixing brands. If you use either there will be a good outcome.

I have no preference for AB in any position, but you will find the drawing from previous Metro kits on placement of the ABs for "tone" which is sort of a defoucusing kind of like analog dithering. 45s do not hiss much in stock form, so no problem with really any of these three choices in those positions. The AB option on Metro kits was to add a little color where all the other Rs were modern film I think?

What transformers are you using and what chassis are you using? Aluminum chassis sound best. 400v and this if using KT66 output tubes -

https://shop.amppartsdirect.com/product ... sformers-1

(address does not reflect product)

I primarily build JTM45/50 models with the mid 50 model rectifier setup (silicon) and higher mains filtering (50u) choosing other nodes filtering based on how it squeezes.

Then you get it built and it seems a little timid because you have heard lots of modern amps driven with all kinds of things..

And the spiral to insanity has you trapped... trapped.. trapped. lol the next thing you know, 1972 mild MP JMP lives in your headbox.

Sort of kidding..

[cdemike]

There are a few people on the Metroamp forum did some comparisons between the brands: https://forum.metropoulos.net/viewtopic.php?t=45545

It seems like there are two schools of thought: that it makes a difference and that it doesn't. Those that think it does make a difference trended towards the Phiers adding more color to the sound akin to how carbon comp is alleged to. I'm not that convinced that the resistors will make a huge difference between manufacturers once you're comparing resistors of the same type (carbon film vs carbon film, metal film vs metal film, carbon comp vs carbon comp, etc.). As I understand it, most JTM45s mostly used carbon film, and as Reeltarded pointed out the specifics depended on what Marshall had on hand that given day, so I'd wager that using one type or the other will get you where you need to be. That said, I do think you can get excellent results using modern carbon film resistors instead.

Maybe it's a double standard, it's and definitely a separate can of worms, but I do firmly believe that capacitor brand, material, and construction make a noticeable difference in an amp's sound -- much more so than resistors (beyond the tendency for carbon comp's values to drive over time and with exposure to heat -- not a concern with a Marshall build anyway, since carbon film is what they used past the very early JTM45s anyway). Those old resistors can get pretty expensive, so I think the main reason to use them would be so the guts look period-correct. If you're looking to nail the sound, I think the money would be better spent on SoZo capacitors (recognizing that's a controversial statement). Of course if you have the resistors already, the resistors you have will always be cheaper than new resistors, so ignore this if that's the case and use whatever allows the cleanest (or most period-correct) lead dress.

Sorry if this comes across as crabby -- I know I'd be burned up if I found out I spent big money on resistors when I didn't need to, so I don't mean it to come across as anything but helpful.

[zephyrblau]

Well, the resistors changed (brand) only when out of stock in any given period. Pihers for JTM45 are expected. Iskras are later. Nothing wrong with mixing brands. If you use either there will be a good outcome.
I have no preference for AB in any position, but you will find the drawing from previous Metro kits on placement of the ABs for "tone" which is sort of a defoucusing kind of like analog dithering. 45s do not hiss much in stock form, so no problem with really any of these three choices in those positions. The AB option on Metro kits was to add a little color where all the other Rs were modern film I think?
What transformers are you using and what chassis are you using? Aluminum chassis sound best. 400v and this if using KT66 output tubes -
https://shop.amppartsdirect.com/product ... sformers-1
I primarily build JTM45/50 models with the mid 50 model rectifier setup (silicon) and higher mains filtering (50u) choosing other nodes filtering based on how it squeezes.
Then you get it built and it seems a little timid because you have heard lots of modern amps driven with all kinds of things..
And the spiral to insanity has you trapped... trapped.. trapped. lol the next thing you know, 1972 mild MP JMP lives in your headbox.
Sort of kidding..

RT;
thanks for chiming in. was not aware of many of the areas you cover esp. Pihers earlier and Iskra later. I've been told that Pihers sound a little dark. (did the switch to Iskra have anything to do w/ the switch to Dagnall trannies ?)
regardless, thanks for the thumbs up! yep... I see on the Metro BOM A-B as 'optional'. wasn't sure what to make of that. thanks for the input. I'll have another look @ those values / positions. any feedback on Drake vs Dagnall regarding reliability ?
I may get in line for a Marstran Radiospares OT. I'm not as picky about the PT nor choke. yes, ALU chassis thank you very much
thanks for filtering input. so noted.
in the grand scheme of things I realize that resistors are a ways down of the list of priorities. (Mr. OT being #1 followed by coupling and bypass caps...) I did land some Mullard .022s @ a decent price but I don't think I'll spring for .68s any time soon.
again my thanks
jerry

[danman]

I got caught up in the same situation as you when planning my first Marshall style builds ten years ago. I went down the rabbit hole buying Piher resistors, mustard caps, Lemco silver mica and many other NOS parts that were used by Marshall. The two amps turned out fine but after building many others since then, I don't hear any difference between the NOS parts and today's modern parts. Marshall used 1/2 watt carbon film in almost every amp with a couple of AB carbon comp resistors here and there when they needed a longer lead to span the turrets. The resistors in the power supply were 1 watt carbon film in most amps. These days I tend to go with 1 watt carbon film or 1 watt metal film (for higher gain amps) for the signal path and 3 watt metal oxide or metal film for the power supply. The new resistors are much quieter than the older ones and I don't hear any difference in the tone myself. For coupling caps, I usually stick with the cheaper Mallory 150's or the Vishay Roederstein MKT1813 and for small value caps, I normally use Vishay 562 series ceramic caps. The Cornell Dublier silver mica are also great caps but the ceramics just seem to sound better and cost much less. Building a clone with period correct parts can be a lot of fun but don't get too hung up on the components because you can still build an excellent sounding amp with modern parts.

[Reeltarded]

Jerry, the Marstran RS will be very good. Awesome matches with that are also made by Heyboer and available at the Amp Parts Direct link for fair money. The JTM45 @400v with increased capacity are my fav PTs. (Heyboer builds Brian's transformers.

About Dagnall vs Drake, most manufaturing choices are made for reasons you can only guess. In that time frame industrial processes required hundreds of switching amplifiers on assembly lines. I bet it has something to do with the distribution deal though.

Roe would know.

As long as your circuit follows the pattern, the voltages are as expected, your OT is correct.. it's really hard to make a bad one.

It is really hard to make great one as well!

The only change that I would make without asking is to double the screens to 1k on the output. I think most of us do that for modern tubes. You can go even higher for fun. It is umm.. squeezy up there.

What are you waiting for! Let's hear it!

I'm Miles, and everying is a sort of Marshall.


M

[WhopperPlate]

I got caught up in the same situation as you when planning my first Marshall style builds ten years ago. I went down the rabbit hole buying Piher resistors, mustard caps, Lemco silver mica and many other NOS parts that were used by Marshall…. I don't hear any difference between the NOS parts and today's modern parts.

Been down the same rabbit hole… and I respectfully disagree…whole heartedly

Iskras are essentially more vibrant and alive with harmonics . Pihers are essentially darker and woodier . One isn’t better than the other.

These do not sound like xicon, koa Speer , Vishay , Multicomp , or anything else modern under the sun .

Reeltarded has it right , the Allen Bradley is for that “defocused analog dithering”, but I find that’s mostly only true within the signal path. If you slap some within the power supply (like the bias feed it b+ dropping R ) you can get some nice harmonic clarity , possibly a more forgiving feeling to play amp ime

With all that said, you can build a great sounding jtm45 amp with new parts…but I would mix and match to taste …I wouldn’t build any amplifier with just one modern brand of resistor. In order to achieve a balanced sound I find a mix essential . This goes for iskras pihers and AB as well

[WhopperPlate]

Building a clone with period correct parts can be a lot of fun but don't get too hung up on the components because you can still build an excellent sounding amp with modern parts.

+1000000

[zephyrblau]

@Miles... I'm with ya brother! I want to hear this thing too but, what I mentioned above re: Mr. OT is that if I order it from Marstran today maybe it'll arrive by June or July. my #1 preference would be Merren but he appears to be MIA for the consumer market.
@WopperPlate thanks for the input. nice idea re: the PS. greatly appreciated.

[Roe]

marshall may have used CC resistors for their long legs, typically as cathode resistors or other resitors that went across the whole the board.

otherwise, it is almost always carbon film, first piher, then iskra, and then later pihers again.

the RS dlx OT differs greatly from the drake -103 (the dagnalls were introduced in late 67 and early 68 on the 100w models)