[Bonddam]

Have an tube amp and need it repaired. I’m in Pennsylvania by NJ. Two resistors burned and having trouble with communication with company from different country. They told me they would send the components but lack of telling me when or am I just getting answers I want to hear.

So anyone please help as I’ve only found stores that deal in guitar amp repair and one store that want deal with this amp due to country who makes it.

I’d replace the resistors myself but unaware of wattage and haven’t looked at the bands to find ohms value.

Pm with info I need please.

 

[tomb]

Have an tube amp and need it repaired. I’m in Pennsylvania by NJ. Two resistors burned and having trouble with communication with company from different country. They told me they would send the components but lack of telling me when or am I just getting answers I want to hear.

So anyone please help as I’ve only found stores that deal in guitar amp repair and one store that want deal with this amp due to country who makes it.

I’d replace the resistors myself but unaware of wattage and haven’t looked at the bands to find ohms value.

Pm with info I need please.

You should post some pics of the resistors and/or your amp's innards. I might be able to tell you the wattage and what may be going on. Do you or the company have a schematic? That would help, too.

You're not going to have much luck, unless you find a repair service that does hi-fi equipment. Even then, tubes are not in the mainstream. That guitar amp repair might be your best bet. They are at least familiar with the principles. Within reason, an amplifier is an amplifier. A guitar amp amplifies for a single channel speaker, but that's about the only difference.*

* There is a pretty big difference in design of the tube operating points, in that guitar amplifiers are meant to over-drive the tubes, resulting in distortion and other artifacts. However, the amplification principles and power supplies work under the same principles.

 

[Bonddam]

Two resistors r20 and r21

 

[tomb]

Those definitely appear to be 2W resistors. You'll actually have trouble finding them at much higher power ratings and have them still fit in that space. Of course, if the mfr of the amp has supplied new ones to you, then that's what you should use.

One trick you can try: It looks like they were soldered flush to the PCB. Of course, that's normal and should not be an issue in most cases. However, if the resistors are truly in need of rejecting a lot of heat, you should solder them with a space between the resistor and the PCB. For resistors of that size, try soldering them so that they're about 1/4" above, but parallel to the PCB. This allows air to circulate in-between.

Sometimes, the actual contact between the PCB and a resistor will cause them to lose a lot of their power rating, because not enough surface area is exposed to air and because flush mounting introduces conduction. Conduction transfers heat better than through air, but if the PCB gets hot as well, this is counter-productive.

Finally, if the resistors they supply burn out again (even after leaving an air space), then you could consider using two resistors in place of one. Power is current-squared times resistance. Using two resistors in series (at half the resistance each) would cut the power in half to each resistor. You can mount two resistors in series as a "teepee" or vertical triangle, with the junction between the two resistors as the pinnacle of the teepee or triangle above the PCB.

 

[tomb]

Also, those resistors appear to be Green, Brown, Black. There should be a fourth band on the other end, but it's probably obscured by the burning. Not to matter, because the fourth band is for the tolerance rating.

So, Green-Brown-Black should be 51 ohms. You'll have to confirm if I'm seeing the colors correctly. Sometimes digital photos can skew the colors, depending on the lighting.

Invest in a cheap DMM, if you can. You can find them cheapest at Harbor Freight, but you can also find very inexpensive ones at Walmart, Home Depot, Lowes, etc. Even the cheapest DMMs will measure resistance accurately - but you must remove the resistors from the PCB, first. Resistors soldered into a PCB may be in parallel with other resistances and the DMM will measure the resistance of the total circuit at those positions, not simply the resistor itself. Removal of the resistor, then measuring it alone with a DMM is conclusive. Don't worry if it measures 50 or 52 ohms - that's simply manufacturing tolerances at play.

 

[Voxata]

I'll help you out on this

 

[Bonddam]

I bought resistors from mouser they have a big selection so got 10 of them. I was lucky the values are written below the each resistor on the circuit board. I was able to research the bands to clarify what was written on the board.
I'll keep you updated after putting new ones in.
Thanks
Bill

 

[jimbop54]

No point in replacing resistors until you know why they burned.

 

[tomb]

No point in replacing resistors until you know why they burned.

Resistors are cheap. As I stated above up there, they may have simply installed them incorrectly and flush with the PCB, negating a lot of convective heat transfer. If they burn out again, then we know that wasn't it and it's time to get it repaired. However, it's probably more than likely it's a shoddy design at that point and repairs are probably not going to help/be too expensive/have little result, etc., etc.

The OP also did not indicate any hesitation at doing this himself, so one could probably conclude that he's capable of it.

 

[Bonddam]

There was a noise when turning on the amp at the rectifier. Eventually led to the resistors blowing. According to George Lenz Ian Wu was blowing out air up my ass telling me I used wrong 274b. Makes sense when I asked if I could use 274b. Ian assumed I ment WE274. Affriad the amp hurt my nice EML 274b tubes.

 

[tomb]

There was a noise when turning on the amp at the rectifier. Eventually led to the resistors blowing. According to George Lenz Ian Wu was blowing out air up my ass telling me I used wrong 274b. Makes sense when I asked if I could use 274b. Ian assumed I ment WE274. Affriad the amp hurt my nice EML 274b tubes.

Yes, that sounds fishy. There shouldn't be any difference between running the 274b or the WE274. Yes, you can do dangerous things when trying to roll tubes into an amp that are different than the amp's design. There are often many tube types that are identical or simply close variations on the same operating parameters. However, if you substitute a tube with significantly different heater currents (or voltage), then yes - you can damage the amp.

Everything I've looked at though, doesn't indicate there's enough difference between a 274 and 274b to make any impact to an amp (anybody's amp designed for the 274).

 

[DenverW]

No point in replacing resistors until you know why they burned.

This ^. A pair of resistors aren't going to do that without a reason. At least you got a good amount of them so you can install a new pair and see if they have the same reaction.