Replacing all resistors in tube amp

[DragonMaster]

I want to replace every resistors in a tube amp for metal film ones, it's just that I have some problems :

-Can I put some 1% resistors to replace 5% and 10% ones?
-I don't want to pay 40$ to change every resistors, because there are 40 different values, and I need to buy 10 resistors each time even if I need only one.

Maybe I'll do the caps first instead. Which ones should I use to replace ceramics?

[Stocker]

Some will tell you that using a different type of resistor will alter the sound of an amplifier...let your ears tell you if it was worth it.

higher precision will almost never hurt anything but your bank account when it comes to selecting components for audio.

Replacing caps that are leaky or dead (esp. electrolytics) will make the biggest improvement unless the rest is just garbage as well.

[Geek]

Originally posted by DragonMaster
Which ones should I use to replace ceramics?

Fiml/foil poly caps are really good. Metallized polyester is lower in quality, but lots cheaper than film/foil and definately better than a ceramic.

[DragonMaster]

I decided to replace the caps finally, especially wax paper ones.

When opening the amp I found two wires short(The wires melt together) that were just before a wax paper cap that already leaked in the preamp circuit.

This cap is in the signal path right before the tape out / power amp in and the first preamp tube.

Also, when I'm selecting tape head, I hear a continuous squeeee, which is so loud I hear it pretty good at minimum volume.

When is was on the kitchen table to see why it had problems, this amp 's tranny compared to the other made a loud hum and vibrated a lot more.

When the volume is at minimum, I hear tons of noise and when on maximum, as much as the other, even if the audio is the lowest at minimum and highest at max.

I think I should replace all the preamp caps because I tested all the tubes and they're all OK.

I'll re-post this in Tubes.

Scheme is at http://users.rcn.com/fiddler.interport/HF12.HTM, click on schematic next to the model name.

[richwalters]

Originally posted by DragonMaster
I want to replace every resistors in a tube amp for metal film ones

Hi there......make sure voltage ratings of this modern stuff is adequate....go for upper wattage ratings, as so much now is quoted at 70°C running which I don't like......Tube amps can tolerate a pretty large out of range working tolerance and function perfectly.......Remember all those amps built in the 50's with plus-minus 25% tolerance with rod resistors perhaps 50% out........and didn't the amps still sound good ?
Alot has been said about resistors/caps changing sound quality.....a noisy res will be noticeable if put in the anode load of a 1st stage but my experience is the components in the NFB loop are the culprits that can change the sound quality-. This area is hotly debated but I find tube amps which use between 15-18dB NFB are best sounding, regardless of the type of component beit polyester/polycarbonate/or S/M.
The earlier Mullard 20 Watt amp (p-p EL34) used 30dB NFB and that sounded tight & unrelaxed and no change of component type made a hoot of difference to the sound quality. I might get bollocked for this....so be it! I never had much respect for magazine articles on this..
The older carbon composition resistors make excellent grid stoppers simply because they are non-inductive, ideal for RF suppression. The earlier waxed silvered mica hold their values pretty well.
However recheck the older values and keep them for grid stoppers around the o/p tubes & UL taps..........This is an area where high mutual conductance tubes (gm or mA/V) can run into parasitic RF oscillation.

Compare the gm of a KT88 with a 6L6 and the 6L6 is as tame as a parrot. Considering the above comment; on the whole I wouldn't replace all the older carbon resistors in sensitive places in an amp unless there is a specific reason for doing so, i.e if they have cooked and values changed in service.


rich

[DragonMaster]

Can poor connection of the case to mains cap be the problem?

Parts being replaced for now(Mouser):
1429-6104 to replace the .1µF wax paper cap that leaked and was next to a short.
1429-6224 to replace a .25µF wax paper that did not leaked but was next to the short.
1430-6333 to replace mains-case wax paper cap.
TVA1711 to replace the old orange electrolytic cap going to the output tubes to speakers tranny.

Now, I have to find replacement for all the small ceramics in the preamp circuit.

BTW, in the scheme, I know mfd represents µF, but what's mmf, pF?

[Stocker]

picoF and mm = nano?

[james_b]

You don't have to buy 10 of each, you can buy resistors in small quantities, even singles, from Welborne Labs, Parts Connexion, Angela Instruments, Mouser and probably others too.

[DragonMaster]

You don't have to buy 10 of each, you can buy resistors in small quantities, even singles, from Welborne Labs, Parts Connexion, Angela Instruments, Mouser and probably others too.

Resistors @ Mouser are min. 10 so I don't change them finally. But some caps can be bought 1 at the time. I'll only buy from Mouser and DigiKey since I'll buy tons of other things from them at the same time.

picoF and mm = nano?

I found after I posted this that mmf is pF, there isn't any pF s in the scheme.

[djQUAN]

mmF is micro micro farad. that's what they call it back then since they didn't have pico farad. but it's the same thing.

uF is 10^-6 F, so uuF or mmF is 10^-12 F, same as pF.