Spreadsheets for Parts Selection & Design Considerations

[ayan]

Hi everyone,

Here are two spreadsheets which I hope some of you will find useful.

1. The first one is just a list of amps I have some documentation on, paying special attention to the type of resistors used throughout the sections of the amp I believe to be more relevant to tone. It is not intended to be comprehensive, it is not complete since I don't have all the information for all the amps listed, and it might have some errors. I think the list speaks for itself, though, regarding where HAD almost always favored metal films (MF) VS carbon film (CF; updated spreadsheet). I find it interesting that as far as grid stopper resistors go, HAD was pretty much 50 -50. Anyway, feel free to edit it adding to it, correcting anything you know to be wrong, etc.

2. The second is a revision to an old spreadsheet I put together some 10 years ago, which I had posted here back in the day, that now has a couple of refinements to address a couple of bugs and add a little more detail. I have used it primarily to conceptualize the differences between my two amps, a 100K Skyliner, similar to 124 but without the "one of" parts (350K trimmer, 250K level and ratio pots, etc.) and a 102 amp. I think it is interesting to see the slight difference in frequency response and gain due to the use of 100K in one of the amps. One other thing I did was to calculate what trimmer setting it would take to set the gain between V1B output and the node between the 100K resistor and pot at the output of V2B. I picked a theoretical number that was close to the documented RF amp setting, 25+K, and it would correspond to an 8dB gain. In turn, the 100K amp would require a 31K to ground trimmer setting to achieve the same gain. However, reality was different since the characteristics of the tubes play a role, etc. Thus, I ended up measuring 6dB between the mentioned points for a setting of about 28K to ground on the 102 amp and close to 30K on the 100K plate amp, and that's where I set my trimmers. Just like in the previous case, feel free to edit, change, correct, etc., and I hope you get some mileage out of this as well. Note that this assumes a pre OD 220K resistor feeding a 100K trimmer unless noted otherwise, a 100K V2A output resistor into a 100K pot unless noted otherwise, and a 150K V2B output resistor into a 100K pot (which is in parallel with a 1 Meg master) unless noted otherwise. In other words, if you use independent masters for clean and OD, you will have to modify the spreadsheet accordingly, etc., etc.

Cheers,

Gil

[martin manning]

Thanks Gil, good stuff. Seems HAD was partial to CC in certain locations on the earlier SN's, but then went to MF on the later ones.

[ayan]

Yes, Martin, but I'd say with a caveat. Most of the amps where he went with MF resistors everywhere are HRMs, while he definitely seemed to stick to CCs for the OD series resistors in the non HRM models and I think CC there make the tone smoother.

G.

Thanks Gil, good stuff. Seems HAD was partial to CC in certain locations on the earlier SN's, but then went to MF on the later ones.

[jelle]

Question: where are the carbon film resistors mentioned in the XLS? For instance, #124 has a bunch of those, and I do not see them listed in the file.

[ayan]

As it turns out, all of the "CC" resistors in the amps listed on the original version of the spreadsheet were carbon film, so it made sense to relabel them; I've updated the attachment to the original post. Personally, I think actual carbon comps are not recommended at all, and Dumble seldom if ever used them, but there are a couple in some older amps.

At the end of the day, for the positions listed, I have obtained best results in non HRM amps using MFs for all plates and cathodes, and the two PI 1 Megs, carbons everywhere else. I have used MFs as grid stoppers as well, I believe I have a mix and match at this time.

In closing, I'm attaching a little picture showing vintage Fender VS Dumble carbon resistors -- comp (Allen Bradley) on the left, and film all others -- so that people who are not familiar with them can tell them apart when looking at amp pictures.

Cheers,

Gil

Question: where are the carbon film resistors mentioned in the XLS? For instance, #124 has a bunch of those, and I do not see them listed in the file.

[martin manning]

Funny I was looking at "CC" and automatically thinking "CF".

[talbany]

The only thing I can add is since the older gen amps with the funky 3 resistor OD entrance network can sometimes benefit by using all CC's there to smooth out the tone since those amps can be a bit gritty at times..On mine I used AB CC's there and on the grids and that amp sounds pretty smooth and still has some clarity..For what it's worth..

BTW..those new Xicon CC's suck IMO..Careful!!

Great info Thanks Gil

Tony

[ayan]

Hi Tony! I haven't bought resistors in probably 9 years. But I had good results with the Xicons CF in the past. Just recently I replaced 3 old NTE MF (they are very nice) in one of my amps in the OD chain (220k, 100k and 150k) with 1W Xicons CF and the OD was noticeably smoother after that.

Cheers,

Gil

The only thing I can add is since the older gen amps with the funky 3 resistor OD entrance network can sometimes benefit by using all CC's there to smooth out the tone since those amps can be a bit gritty at times..On mine I used AB CC's there and on the grids and that amp sounds pretty smooth and still has some clarity..For what it's worth..

BTW..those new Xicon CC's suck IMO..Careful!!

Great info Thanks Gil

Tony

[Max]

.. some clarity ..

I've attached two pictures of the resistors in a Dumble amp famous for clarity. Picture source: http://personalpages.manchester.ac.uk/s ... 20%230003/

Cheers,

Max

[talbany]

Hi Tony! I haven't bought resistors in probably 9 years. But I had good results with the Xicons CF in the past. Just recently I replaced 3 old NTE MF (they are very nice) in one of my amps in the OD chain (220k, 100k and 150k) with 1W Xicons CF and the OD was noticeably smoother after that.

Cheers,

Gil

Hey Gil
I agree.The Xicon carbon films are not bad (although I have gone through my share of bad ones) I was referring to the Xicon Carbon comps..

Tony

[talbany]

.. some clarity ..

I've attached two pictures of the resistors in a Dumble amp famous for clarity. Picture source: http://personalpages.manchester.ac.uk/s ... 20%230003/

Cheers,

Max

Hello Max
I think you may have taken my comment beyond it's context.. I was referring to how certain resistors sound (comparatively speaking) in a given circuit in a particular amp (my 2nd generation variant) and not a Winterland..Different amp design!! ..So my question would be if you put in all metal film resistors in the Winterland would that amp have even a higher (possibly too much) level of clarity?,(Remember it has the Williamson Hi FI phase inverter) ..IMO I think it would! (less noise)..If so would you like the sound of the metal films vs carbon composites in a Winterland?..This is the generalized statement I was making in my earlier post..BTW..I think the Williamson PI has much to do with the clarity of that Winterland..
In the end all of this really is just my opinion..Some will agree with me and some will not..Getting into a debate about how resistors sound to each of our ears in a given audio system and have everyone agree has been attempted and failed here on numerous occasions...
Have a great day
Tony

[glasman]

1W carbon films are my favorite. Either XICON, TE, KOA or a few others.

Of course I am not striving to make copies of some particular Dumble.

I went through my Metal Film stage. No sonic nirvana there. Neither were XICOM MPP caps lol.

I have been testing some of stacked polyester caps as of late and the results have been very favorable. The only down side is that you really cant test them for polarity. Still need to do a bit more live proximity testing to see effects.

[10thTx]

Guys, I appreciate the info about the 1w carbon films.

I ordered some the other day and plan to try them on the overdrive channel of my D'Mars ODS which uses a 5879. I'll try to remember to report whatever difference or not difference I hear in the OD after installing them. I think the 5879 is a remarkably touch sensitive tube but it is a tad chimey on the high end.

I changed all the resistors in the OD section of my D'Mars ODS to Xicon carbon film 1w resistors except the plate and cathode resistors. It did make a difference and is significantly smoother.

Thanks for the tip!

With respect, 10thtx