Silverface Fender Twin has nasty bass distortion

[amgard]

Almost lost my beer laughing. It definitely happens. Trying to interpret resistor color codes when slightly off colors are used as markings. Funny and frustrating at the same time.

Have to sympathise here. I've opened up a new pack of 2.2k resistors and they have red bodies!

[gtrplayr1976]

Bob: page 2 of this pdf: http://music-electronics-forum.com/a...win_rev-2-.pdf The blue layout drawing shows the 2 resistors at the filter caps in the lower left of the layout drawing. To the right of the 100K it says "10 vibrato controls"

Another typo, wire #10 then reappears below ch.1 middle pot, going where it should, to V2 plate resistors.



I've never seen such a drawing either, I thought it was an original blueprint type, do you think it's bogus? Here's another with all the same drawing, revision, and ECO numbers, yet the values are corrected. [ATTACH]22702[/ATTACH]
I assumed it was edited as it looks like a custom pdf (still has the "10 vibrato controls" typo), sorry to further confound this convoluted issue, I think I've had enough of it .

THANKS for this layout ! I use the layout to help me learn more about the schematic. I'll NEVER again use them to replace parts.

[gtrplayr1976]

As I had stated before. The SF Twin I am working on is a 73 with push/pull MV . Neither the schematic nor the layout totally match what I am seeing in this amp. I have been replacing parts with what I see in the amp.

[amgard]

I might be missing something, as I usually only look at the schematics, but both of those layouts show a SPST switch on the back of the MV, whereas the schematic needs a DPST to do the job?

[gtrplayr1976]

That's what I was thinking. The difference between yellow and orange is 10x. Well, that's good news! The problem may be solved.

Trouble reading resistors is why I recommended clamping an ohmmeter across the resistor to see what was originally there. One thing that I've learned over the years is that it's hard for me to trust my eyes, my memory, schematics and especially layout diagrams. I've encountered errors attributable to all of them. Just as a matter of course, when I go through an amp I print out a schematic and write the pre-service parts measurements and voltages on it. Then I print out another one for the post-repair assessment. That way I always have before/after documentation, so I don't have to rely on memory.


Personally, I find that reading resistor values is getting harder and harder. And I'm not just referring to similar colors like yellow and orange, which can be hard to tell apart on an old CC resistor that's been subjected to heat and the resulting discoloration. Today the resistors are shrinking. Today it looks like the manufacturers are shrinking the size of the through-hole parts down to the scale of the SMD parts, to the point that 500mW resistors are impossible to read without a magnifying loupe. For example, these are all current production 500 mW metal film resistors. Some are a lot harder to read than others:

[ATTACH=CONFIG]22696[/ATTACH]

http://music-electronics-forum.com/t21277/

As a result of the shrinking resistor sizes, I find that I have too much trouble reading those flea-sized 5-band resistors, so I just sort them with an ohm meter when I get them mixed up.

How in the world do you know the wattage if the sizes are different ?

[bob p]

How in the world do you know the wattage if the sizes are different ?

organizational skill.

But seriously, now that 500mW resistors are so small, there's no reason to order 250mW resistors, so I just buy everything with larger power ratings. 1W MF resistors are pretty small and have better specs. If you buy the majority of your resistors in a single power rating, there isn't much sorting to do.

I also sort/organize my resistors. I don't mix them up. There's a thread around here somewhere, where we've been discussing how to store resistors. A common method is the coin envelope. Someone recommended clear baseball card sleeves. My supplier delivers the resistors in snack-sized ziploc baggies that are just big enough to fit a snippet off of an ammo reel. They come with a pre-printed label attached to the baggie that has all of the part's specs printed on it, including the resistor's value, power rating, manufacturer's part number, supplier's part number, etc. That makes sorting, storage and re-ordering very easy.

[gtrplayr1976]

organizational skill.

But seriously, now that 500mW resistors are so small, there's no reason to order 250mW resistors, so I just buy everything with larger power ratings. 1W MF resistors are pretty small and have better specs. If you buy the majority of your resistors in a single power rating, there isn't much sorting to do.

I also sort/organize my resistors. I don't mix them up. There's a thread around here somewhere, where we've been discussing how to store resistors. A common method is the coin envelope. Someone recommended clear baseball card sleeves. My supplier delivers the resistors in snack-sized ziploc baggies that are just big enough to fit a snippet off of an ammo reel. They come with a pre-printed label attached to the baggie that has all of the part's specs printed on it, including the resistor's value, power rating, manufacturer's part number, supplier's part number, etc. That makes sorting, storage and re-ordering very easy.

That's how I've been getting mine..ALTHOUGH..take a look at the ones I just got Isn't there certain wattages you need to use for a particular application ?

[bob p]

Isn't there certain wattages you need to use for a particular application ?

Almost all of the resistors that you find in amp schematics are 500mW resistors by default; that is, unless the schematic says otherwise. Many times a 500mW resistor is actually higher than what is needed , but for the sake of uniformity they will use all 500 mW resistors. In some cases where the resistors dissipates very little power it's actually safe to substitute a 250mW resistor if that's all you have. Because I like MF resistors, and because the size of the quality 500mW resistors is shrinking, I just buy small 500mW resistors and I don't buy 250mW resistors any more. That gives me one less category of parts to worry about.

When it comes to standardizing your stockpile, It never hurts to use a resistor with a higher wattage rating, provided it will physically fit wherever you need to put it. The good thing about using resistors with higher wattage ratings is that they tend to be rated for higher voltages, and they tend to be lower noise. For example, I recently subbed 1W resistors for 250 mW resistors in a stompbox build. The new 1W MF resistors are the same size as the old 250mW resistors, and it was no problem to fit them in a 0.4" space.

[gtrplayr1976]

Most of what I have are 500 mW ,but I do have a few 250 mW , some 1s,2s, and 3s and a few 5 watt power resistors.