196 Bandmaster Amp Blew Capacitors Need Help

barnett468

Member
Messages
92
Hello;

New to the Forum . Saw several threads here and it looked like a very good place for info . My apologies if this is in the wrong section.

I just bought a 100% all original late 62 bandmaster amp . I plugged it into a variable transformer . I out the transformer on 20 volts and turned the amp power on . I slowly turned the voltage up to 110 . After 2 minutes I turned the standby switch on . After around 2 minutes there was a poof sound and some smoke . The amp was not plugged into a speaker cabinet at the time.

I took the amp out of the cabinet and all the capacitors on the bottom look good . I saw some dark brown fluid leaking out of the 4" x 10" cover over the 6 big capacitors and 2 of them on one end look like they are leaking and the tops are distorted outward slightly.

1. Did I kill the amp by not having it plugged into a speaker cabinet?

2. What section of the amp do these capacitors control?

3. Will using a different type of capacitor in this section change how it will sound?

4. Does anyone know where I can get original capacitors? I realize other ones may be leaking to some degree also but I want to keep the amp 100% original if at all possible even if there is a little degradation in the sound quality.

5. I live in the Riverside area of Southern California . Does anyone know anyone nearby that can properly repair it instead of someone that will simply change all the capacitors just because they are old?

Thanks in advance for any help.
 

Elantric

Member
Messages
12,410
1. Did I kill the amp by not having it plugged into a speaker cabinet?

Possibly - typically occurs if you feed input signal (or play guitar) into the amp with no speaker load.

Without a load (i.e. no speaker ), high currents build up internally and weak parts on a 54 year old amp can smoke, or carbon arcing can occur between components on the B+ Voltage rail

regardless - inspect the amp for burnt parts, and get familiar with the circuit.
I took the amp out of the cabinet and all the capacitors on the bottom look good . I saw some dark brown fluid leaking out of the 4" x 10" cover over the 6 big capacitors and 2 of them on one end look like they are leaking and the tops are distorted outward slightly.
Inspect the large electrolytic caps and 1 watt resistors under the steel "ice cube tray" under the chassis

the large caps are [email protected]
My sources for parts are
https://www.tubesandmore.com/
https://www.cedist.com/
http://www.mojotone.com/



http://www.cnjradio.net/fndramp2.html

bandmaster_6g7-a_schem.gif

TF4UCuuRREmm9pa19xTFBQ.jpg


16340168426_78a6f0b89d_o.jpg
 
Last edited:

Elantric

Member
Messages
12,410
5. I live in the Riverside area of Southern California . Does anyone know anyone nearby that can properly repair it instead of someone that will simply change all the capacitors just because they are old?

call these guys
and compare prices

and visit them

Noise Electronics  
Address: 1440 3rd St #4
Riverside, CA 92507
Phone: ( 951) 295-8101



Music Mikes
6511 Magnolia Ave
Riverside, CA 92506
Phone: ( 951) 683-7777
 
Last edited:

0018g

Member
Messages
1,901
You may have damaged your amp, and by asking these questions I fear you might damage yourself. Lethal voltage in one of these, but beyond that it's too cool and valuable to get the iron smoked by an inexperienced tech.

If you must do it yourself, get some of that Youtube education and make DAMN sure you know how to safely deal with filter capacitors and troubleshooting a hot amplifier.

PS-even if you can find NOS caps, they're no good. Spring for Spragues if you can still get 'em.
 

VaughnC

Silver Supporting Member
Messages
19,036
A tube amp can be turned on with no speaker connected as long as there's no signal into the amp or it's not in self oscillation to cause flyback. However, most tube amps have shorting type speaker jacks to prevent flyback voltage damage if you forget to plug in a speaker cable.

As far as capacitors go, you cannot always tell if they are bad by just looking at them. However, electrolytic caps should be replaced about every 10-15 years to prevent possible damage to other irreplaceable components. Sometimes an old power transformer will blow before the fuse when an aged cap shorts.

Be very careful inside a tube amp as there's upwards of 450 lethal volts waiting to grab you. The electrolytic capacitor's job are to filter the high voltage power supply, which powers the whole amp. And this is no place for novice fingers.

Good luck!
 

barnett468

Member
Messages
92
Thanks for the info guys

I have zero interest in fixing it myself.

Thanks, I am at least aware not to touch anything, especially capacitors.

The guitar chord was plugged into the amp but not into the guitar.

Elantric, do any of the places you listed have any original orange astron capacitors . My bad ones are MM-20-525
 

Elantric

Member
Messages
12,410
It's best to communicate your wishes to the repair shop , they should be able to take pics of their work and verify you obtain similar OEM spec parts
 

gldtp99

Member
Messages
4,529
NOS electrolytic capacitors are usually too old to be used in a working amp----- they're fine for a museum piece that will never be powered up----it doesn't matter who might have "reformed" them--- they are old ----- Electrolytic capacitors have a finite working lifespan so one should use new capacitors when replacing them.

Like these: https://www.tubesandmore.com/products/capacitor-ft-500v-axial-lead

This work needs to be done by someone who knows what they are doing as far as working inside High Voltage tube audio equipment----- this is no place for an "oopps, I guess I did it wrong or something, why is my house on fire ?"
 

barnett468

Member
Messages
92
NOS electrolytic capacitors are usually too old to be used in a working amp----- they're fine for a museum piece that will never be powered up----it doesn't matter who might have "reformed" them--- they are old ----- Electrolytic capacitors have a finite working lifespan so one should use new capacitors when replacing them.

Like these: https://www.tubesandmore.com/products/capacitor-ft-500v-axial-lead

This work needs to be done by someone who knows what they are doing as far as working inside High Voltage tube audio equipment----- this is no place for an "oopps, I guess I did it wrong or something, why is my house on fire ?"


my preference is to have it 100% original . not all 50 year old caps will be bad and i couldn't care less what i have to pay for good original ones . i can buy reworked bandmasters all day long and would have done so if i wanted a non original amp . i am more of a collector and it will get very little use.
.

.
 

barnett468

Member
Messages
92
Well, I completely disagree with your approach

don't really care if you disagree with my approach because my goal is obviously different than yours . i will change to different capacitors if i have to but if i dont have to then i won't . i have 2 other amps that i use for playing so i don't "need" this one to play through and did not buy it to play through on a regular basis
 
Last edited:

logdrum

Member
Messages
2,123
Sorry to hear. Did you just forget to connect the amp to the speaker load. Really did not expect since you actually slowly powered it up with a variac. I triple check on day to day basis and would probably check it more than that if I had an old amp like that.
 

0018g

Member
Messages
1,901
But if it is EVER turned on, you need NEW capacitors. A bad filter cap can take out a power transformer, and then you've really screwed up the value.

not all 50 year old caps will be bad

Yes they will. They dry up over time. Simple as that.

You claim to know nothing about this, yet you insist on the concept of "50 year old new caps are fine. They're still NEW". You're right-you are clueless about working on these.

Your "goal" seems to be seriously jeopardizing a fine old amplifier. If you must, the new caps can be fitted into the old outer shell of the original caps(modern caps are smaller). This way, you're not installing junk in your amp but it still appears "original".
 




Trending Topics

Top Bottom