DeArmond Model R5

[Chevyreb]

OK thanks I got it... I see which one it is. I'll look at the transformer to verify hot side.

So When I replace the cord I can discard the dead cap altogether then correct? I know to make sure its discharged first. Vocational Heat and air guys in high school used to play bad tricks with start capacitors

[Firestorm]

Second. Is the cathode resistor and the cathode bypass cap on the 6V6 the ones circled in the schematic pic below labeled #1? If so do I need to test them in the circuit with power applied (tubes in or out?) reading voltages from the voltage chart in the schematic, or do I need to remove one side of the resistor and check that with ohm meter? I am assuming these can be tested without the power tube since it has apparently quit working?

Yes, #1. I wouldn't even bother testing them (resistors used in that position will likely have drifted in value; they also frequently change value with temperature). Just replace it with 470 ohm 2 watt resistor (330 was a bit small to begin with, IMO). Modern 25/25 caps are inexpensive and quite a bit smaller, too.

Third, Is the new can cap (the big metal one) and filter cap one and the same? If not please assist in identifying them each.

Yes, that is all the filter caps in one "can." The symbols (square, half circle, triangle) represent the different sections. You will not find these exact values available anymore. Something similar can be had (expensively) from Antique Electronics Supply. Or single caps of the same values can be used instead.

Lastly...at least for now, is the area circled labeled #3 the tremolo circuit that is absent from my plain r5 amp?

Yes.

[Chevyreb]

First off thanks Firestorm!

Second. Is the cathode resistor and the cathode bypass cap on the 6V6 the ones circled in the schematic pic below labeled #1? If so do I need to test them in the circuit with power applied (tubes in or out?) reading voltages from the voltage chart in the schematic, or do I need to remove one side of the resistor and check that with ohm meter? I am assuming these can be tested without the power tube since it has apparently quit working?

Yes, #1. I wouldn't even bother testing them (resistors used in that position will likely have drifted in value; they also frequently change value with temperature). Just replace it with 470 ohm 2 watt resistor (330 was a bit small to begin with, IMO). Modern 25/25 caps are inexpensive and quite a bit smaller, too.

Does changing this to a higher resistance value change the BIAS of the amp? Interested to understand why/how this effects the circuit/sound? I assume I should be looking for a 1% resistor?

Third, Is the new can cap (the big metal one) and filter cap one and the same? If not please assist in identifying them each.

Yes, that is all the filter caps in one "can." The symbols (square, half circle, triangle) represent the different sections. You will not find these exact values available anymore. Something similar can be had (expensively) from Antique Electronics Supply. Or single caps of the same values can be used instead.

OK I understand I can replace the can with several resistors...I need to trace the leads from the can to determine which values are used where. Also which type caps should I get?


Apparently this is the subject of some debate?

I found this while surfing...

http://www.diyaudio.com/forums/tubes-va ... e-amp.html

"2W metal film resistors are unlikely to sound much quieter than 2W carbon films, and carbon films generally sound "warmer"- so you may get the opposite of what you want! Carbon comp resistors can be quite noisy, but if they're in the 3rd/4th stage you should be ok. Wirewound resistors are great if you can afford it, but hardly necessary for a guitar amp.
As for caps, any poly type will do, although film types are preferred over metallized types. Teflon or polystyrene is the best, although polypropylene is more common. In a guitar amp you probably won't notice the difference though. Some people also like to add a ceramic cap in parallel with coupling caps, to give some high-freq texture.

I agree with Tweeker about cathode bypass caps- avoid electrolytics if you possibly can, and use non-polarized ones if you have to. However, in a guitar amp you can safely reduce the cathode bypass caps to 1uF or 2uF, thus allowing you to use poly-type caps. The lower value will really tighten up and smooth out the bass tone too!"

Lastly...at least for now, is the area circled labeled #3 the tremolo circuit that is absent from my plain r5 amp?

Yes.

[Firestorm]

Does changing this to a higher resistance value change the BIAS of the amp? Interested to understand why/how this effects the circuit/sound? I assume I should be looking for a 1% resistor?

Well, it kinda sorta changes the bias, but the amp is going to run in Class A no matter what you put there so the intent is just to cool the tube slightly. This amp is essentially a Fender Champ, which always ran 470 as the cathode R. That, plus the increase in wall voltage over the years made me suggest it. No need for 1%, 10% would be fine. Carbon comps were traditional (noisy, but in the cathode circuit so it doesn't much matter). Hard to find these days larger than 1W (I might have some, tho). Carbon films are readily available. Ohmite makes a nice ceramic comp resistor that works here, too.

OK I understand I can replace the can with several resistors...I need to trace the leads from the can to determine which values are used where. Also which type caps should I get?

Not resistors, caps. For the sake of "originality," you should replace with another "Mallory FP type" which AES has (if they're in stock). There is a 40/20/20 for $30 or so that would be fine. Don't try the JJ 40/20/20/20; too big, won't fit the hole and needs a clamp anyway. You may not need to do this right away. If the cap is going south, it will make the amp hum unacceptably. If the hum is not too bad, you can probably wait a little. Check the dropping resistors attached to the cap can; if they are overheating, it may be a sign the cap is beginning to short. Time to replace the cap for sure in that case. These caps can be hard to work with. You need a very large soldering iron to get the old one out and the new one in.

[NickC]

OK thanks I got it... I see which one it is. I'll look at the transformer to verify hot side.

So When I replace the cord I can discard the dead cap altogether then correct? I know to make sure its discharged first. Vocational Heat and air guys in high school used to play bad tricks with start capacitors

Yes, you can snip the "death cap" out and eliminate it from the amp (save it, might be able to use it in the future).

It is not an electrolytic cap, so you don't have to worry about it holding a charge; it won't zap you. But you are wise to always play it safe with caps; better safe than sorry.