ok, so to sum things up.
this is so far what I should do:
1.Test with known good tubes.
2.redo The ground connection to the brass plate in image 4834
3.replace all cathode bypass caps (25uF/25V or higher)
4.rewire heaterwires for correct polarity
5.measure resistance from beginning to the end of every wire
6.The trem ticking is common and easy to fix, you shouldn't have to replace the Optocoupler. With the chassis in front of you, rear chassis facing you look at the Optocoupler, the black thing with four leads coming out of it. The lead closet to you on the left will have a 10 Meg resistor connected to it. To the left of this connection is a 25uF capacitor. What you want to do is install a .01 capacitor (400 to 600V rating) between the 10 Meg resistor connection and the ground connection of the capacitor. This should solve your ticking problem.
7.replace critical bias circuit parts. which would include:
a. that metal can diode (replace with 1N4007)
b. remove the 1K5 resistors from the tube sockets; and replace with metal film of the same value 1Watt. I like to solder the resistor to the wire and shrink wrap it then solder the other end directly to pin 5. (1k5 0.5W metal films are fine for the grid stoppers); when you mount the resistor to pin 5 cut the lead short, bend it around the eyelet so that there is a good mechanical connection with zero lead length between the resistor body and pin 5, Then solder it in place.
c. replace the 220K bias feed resistors with metal films too. Matching these resistors isn't a bad idea either. 1W? It's best to match the 1K5 grid stoppers and the 220K bias feed resistors so that each tube is getting the same bias voltage.
8.Replace the carbon comp Screen resistors with 1K/5W wirewounds.
9.Redo AC powercord connection.
10.Check all your ground connections with an ohm-meter, any high readings should be reconnected and re-soldered with new solder.
any more thoughts or suggestions?
btw is it interesting to use shielded wire for the inputs?
And also place the 68K input resistors near the tube instead of at the inputjack?
Is it interesting to replace the ceramic disc caps (tonestack and brightswitches) with silver mica caps? Or just leave it like it is?
Thanks
1966 Bandmaster Blues
Moderators: pompeiisneaks, Colossal
Re: 1966 Bandmaster Blues
Nice amp. A picture of your OT would be nice to verify if original.
I would Not replace the carbon comp resistors with Metal films. I would measure them , if they are close to spec I would leave them . They sound better . You will not hear any reduction in noise unless they are bad. Obviously the screen grids have been replaced already, with the doubled 1K , 1 or 2 watt. I personally like the 470 ohm 1 watts , as they can act like a fuse if the tube shorts. Same goes for the carbon comp control grid resistors, They almost never fail and seldom go bad, I have never found them to contribute to any noise issues.
channel one has obviously had a volume pot changed, so I would check the wiring there very carefully. You will need an 80w iron to redo the ground on the front ground plane.
Many people feel the ceramic caps contribute to the sound qualty of these amps. So don't be too quick to scrap them. I personally prefer polystrene .
I almost never change the preamp cathode bypass caps, I find unless they are bad, no reason to. They don't see much voltage and tend to last a very long time.
Sometimes it helps to wire the heaters the same. Sometimes it makes no difference. If you hear a constant hum and the power supply and bias supply is good , then try rewiring the heater polarity. If the amp is quiet already leave it.
This is not a Hi gain preamp and shielded input wire is not really necessary, but lead dress is. If the preamp is too lively and it is not a tube, try moving the input lead a little, make sure it crosses 90 degrees the other leads and is not touching anything. And never close to the heater wires. Shielded wire will negatively impact the tone as well, but it is a quick fix . If you use shielded wire, only ground one side, The input side.
Bottom line , Keeping this amp as original as possible will be in your best interest. Sound wise and sale wise.
The front grill has been redone, too shiney. You can find better looking/aged material, or even a piece of original or used cloth.
I see it has JJ power tubes what are the preamp tubes?
If the OT has been changed and or it is the reason for the low output, you might like a Bassman OT . One side of the Output tranny being bad may cause the low power . It is not uncommon for bandmaster to have blown OT's. They are a bit weak.
I would Not replace the carbon comp resistors with Metal films. I would measure them , if they are close to spec I would leave them . They sound better . You will not hear any reduction in noise unless they are bad. Obviously the screen grids have been replaced already, with the doubled 1K , 1 or 2 watt. I personally like the 470 ohm 1 watts , as they can act like a fuse if the tube shorts. Same goes for the carbon comp control grid resistors, They almost never fail and seldom go bad, I have never found them to contribute to any noise issues.
channel one has obviously had a volume pot changed, so I would check the wiring there very carefully. You will need an 80w iron to redo the ground on the front ground plane.
Many people feel the ceramic caps contribute to the sound qualty of these amps. So don't be too quick to scrap them. I personally prefer polystrene .
I almost never change the preamp cathode bypass caps, I find unless they are bad, no reason to. They don't see much voltage and tend to last a very long time.
Sometimes it helps to wire the heaters the same. Sometimes it makes no difference. If you hear a constant hum and the power supply and bias supply is good , then try rewiring the heater polarity. If the amp is quiet already leave it.
This is not a Hi gain preamp and shielded input wire is not really necessary, but lead dress is. If the preamp is too lively and it is not a tube, try moving the input lead a little, make sure it crosses 90 degrees the other leads and is not touching anything. And never close to the heater wires. Shielded wire will negatively impact the tone as well, but it is a quick fix . If you use shielded wire, only ground one side, The input side.
Bottom line , Keeping this amp as original as possible will be in your best interest. Sound wise and sale wise.
The front grill has been redone, too shiney. You can find better looking/aged material, or even a piece of original or used cloth.
I see it has JJ power tubes what are the preamp tubes?
If the OT has been changed and or it is the reason for the low output, you might like a Bassman OT . One side of the Output tranny being bad may cause the low power . It is not uncommon for bandmaster to have blown OT's. They are a bit weak.
Re: 1966 Bandmaster Blues
I just reread you first post . Regarding the OT numbers. It cannot be the original. The date code is wrong for your amp. But it might be a bandmaster OT from 1970. 1960 would be all wrong. Like I said, Bandmaster OT's are too weak and blow, so I would measure it or replace it with a known good one. Or better yet, just put a replacement Blackface Bassman OT in there.
Re: 1966 Bandmaster Blues
billyz, thanks for your reply.
Food for thought for sure.
I still need to get it working properly.
Especially the first channel. since there is no sound from it.
What would a replacement Blackface Bassman OT do to the sound?
Give it more headroom?
The preamptubs are: V1 = GE7025, V2 = GE7025 V3= Groove tubes 12AX7A, V4 = Adzam ECC81.
J
Food for thought for sure.
I still need to get it working properly.
Especially the first channel. since there is no sound from it.
What would a replacement Blackface Bassman OT do to the sound?
Give it more headroom?
The preamptubs are: V1 = GE7025, V2 = GE7025 V3= Groove tubes 12AX7A, V4 = Adzam ECC81.
J
Re: 1966 Bandmaster Blues
The Bassman tranny will give a better quality low end and a beefier tone. The high end is just as good and the midrange is nice and thick. Might also be louder. There are many good aftermarket OT's. I probably would not spend the bucks for a Mercury Magnetics. Check MOJO or Antique Electronics.
If you are going to change the resistors and ceramic caps then I would go all the way and convert over to EL34's. The tone is Righteous on every el34 modded blackface amp I have ever worked on. The power tranformer can handle the extra current, no problem.
Don't get me wrong, I am for keeping them as close to original as possible. But, in the end it is your amp and you can do what ever you want. I usually reserve the El34 conversion to amps that are in poor condition to start with or the customer wants it.
Mainly I am in the minority on the Metal film resistors and other (upgrades) .
I have done them and am no longer a fan. I always feel the amp lost some soul afterwards and no improvement in noise.
If you really want some good sounds go for a good set of USED vintage RCA 6l6's, or similar( think KT 66). Make sure they are pretty close in Current draw. The preamp tubes should be ear tested. I find Telefunken, Mullard, Amperex, RCA are my favorites. I like JAN or closely matched Phase invertor tubes( 12at7). Use the JJ's/sovtek/chinese for the tremolo or other channel you don't use.
If you are going to change the resistors and ceramic caps then I would go all the way and convert over to EL34's. The tone is Righteous on every el34 modded blackface amp I have ever worked on. The power tranformer can handle the extra current, no problem.
Don't get me wrong, I am for keeping them as close to original as possible. But, in the end it is your amp and you can do what ever you want. I usually reserve the El34 conversion to amps that are in poor condition to start with or the customer wants it.
Mainly I am in the minority on the Metal film resistors and other (upgrades) .
I have done them and am no longer a fan. I always feel the amp lost some soul afterwards and no improvement in noise.
If you really want some good sounds go for a good set of USED vintage RCA 6l6's, or similar( think KT 66). Make sure they are pretty close in Current draw. The preamp tubes should be ear tested. I find Telefunken, Mullard, Amperex, RCA are my favorites. I like JAN or closely matched Phase invertor tubes( 12at7). Use the JJ's/sovtek/chinese for the tremolo or other channel you don't use.
Re: 1966 Bandmaster Blues
Picture IMG_4822 shows the bug, or optocoupler, wrapped in black electrical tape--a sure sign that what's there ain't working right. Just get a new one.
The voltages look like they're in the right ballpark. The B+ on the power tubes is a wee bit low, but not out of bounds for a Fender of this age.
I've worked on lots of Fenders, and my general rule of thumb is: don't replace what you don't really need to.
The dual cell cathode capacitors are optional to replace. If they leak DC, the worst that happens is you lose gain on that preamp stage.
A key tool in amp work, particularly Fenders--since they are so logically laid out--is a signal probe. Make two--trust me, they are worth their weight in gold. Here's how:
For each, get a wooden chopstick, or equivalent non-conducting stick, a 1/4" plug, a 3 to 6 foot long length of shielded cable (or just cut a sacrificial instrument cable in half), a good 630V signal capacitor--almost any value will do, an alligator clip, hook up wire, some tape and some shrink.
1. Attach the alligator clip to the end of about 18" of flexible hookup wire.
2. Attach the 1/4" plug to one end of the shielded cable--center conductor to tip, shield to shaft. This is already done if you use a guitar cable.
3. At the other end of the shielded cable, strip a bit of the center conductor, and solder it to one lead of the capacitor.
4. Solder the free end of the clip lead to the shield.
5. Use shrink tubing and electrical tape to affix the cable/capacitor to the chopstick, so the free lead of the cap sticks out past the chopstick by about an inch.
Now you have your probe. The capacitor keeps high volts from the amp from damaging whatever you have the probe plugged into.
Here's how you use it.
In your amp, you said that channel 1 doesn't work. OK, so plug a signal, like from a cd player or radio headphones, into the input jack. Plug the 1/4" end of the probe into another amp, and clip the alligator clip to the chassis of the amp under test. Now, using the exposed end of the probe, start touching points along the signal's path, starting at the input jack. Do you hear the input sound? If so, move to pin 2 of V1. Still Sound? If so, good, move to pin 1. Keep moving downstream until you find a point where there's no sound, at which point you are closing in on the fault.
You can also use the probe to inject signal. Connect the Bandmaster speaker output and operate the amp. Plug the cable of the probe into the headphone output of your source, and use the probe end to inject signal. Start at the power tubes and move upstream. As you go, the sound you hear from the amp should get progressively louder as you move your injection point into more gain stages.
Welcome to the wonderful world of troubleshooting.
The voltages look like they're in the right ballpark. The B+ on the power tubes is a wee bit low, but not out of bounds for a Fender of this age.
I've worked on lots of Fenders, and my general rule of thumb is: don't replace what you don't really need to.
The dual cell cathode capacitors are optional to replace. If they leak DC, the worst that happens is you lose gain on that preamp stage.
A key tool in amp work, particularly Fenders--since they are so logically laid out--is a signal probe. Make two--trust me, they are worth their weight in gold. Here's how:
For each, get a wooden chopstick, or equivalent non-conducting stick, a 1/4" plug, a 3 to 6 foot long length of shielded cable (or just cut a sacrificial instrument cable in half), a good 630V signal capacitor--almost any value will do, an alligator clip, hook up wire, some tape and some shrink.
1. Attach the alligator clip to the end of about 18" of flexible hookup wire.
2. Attach the 1/4" plug to one end of the shielded cable--center conductor to tip, shield to shaft. This is already done if you use a guitar cable.
3. At the other end of the shielded cable, strip a bit of the center conductor, and solder it to one lead of the capacitor.
4. Solder the free end of the clip lead to the shield.
5. Use shrink tubing and electrical tape to affix the cable/capacitor to the chopstick, so the free lead of the cap sticks out past the chopstick by about an inch.
Now you have your probe. The capacitor keeps high volts from the amp from damaging whatever you have the probe plugged into.
Here's how you use it.
In your amp, you said that channel 1 doesn't work. OK, so plug a signal, like from a cd player or radio headphones, into the input jack. Plug the 1/4" end of the probe into another amp, and clip the alligator clip to the chassis of the amp under test. Now, using the exposed end of the probe, start touching points along the signal's path, starting at the input jack. Do you hear the input sound? If so, move to pin 2 of V1. Still Sound? If so, good, move to pin 1. Keep moving downstream until you find a point where there's no sound, at which point you are closing in on the fault.
You can also use the probe to inject signal. Connect the Bandmaster speaker output and operate the amp. Plug the cable of the probe into the headphone output of your source, and use the probe end to inject signal. Start at the power tubes and move upstream. As you go, the sound you hear from the amp should get progressively louder as you move your injection point into more gain stages.
Welcome to the wonderful world of troubleshooting.
Rich Gordon
www.myspace.com/bigboyamplifiers
"The takers get the honey, the givers get the blues." --Robin Trower
www.myspace.com/bigboyamplifiers
"The takers get the honey, the givers get the blues." --Robin Trower
Re: 1966 Bandmaster Blues
As for your channel not working , check the solder joint where the black lead is soldered to the 220k mix resistor. It looks funky. also check the joints on the first preamp tube socket. It is hard to see but one of them looks suspicious too. of course test the tube. just swap it for a known good one.
The signal probe setup is a very good tool. I usually just do a POP test.
The signal probe setup is a very good tool. I usually just do a POP test.
Re: 1966 Bandmaster Blues
Lots of mojo ready to be released in there. I would change the cathode bypass caps and fix that nasty solder blob on the brass plate before anything else. Those caps could leak DC, leak electrolyte, or have low capacitance. Keep them in a bag for posterity.
Trem tube plates should read high when the trem switch is not activated since their grids are very negative preventing current in the "Trem off" mode.
Trem caps don't look original which is fine if the speed range is good.
Not sure if it was mentioned but you can switch the 1st 2 small tubes to see if the dead channel comes to life, (and the other one goes silent from a bad tube.)
Trem tube plates should read high when the trem switch is not activated since their grids are very negative preventing current in the "Trem off" mode.
Trem caps don't look original which is fine if the speed range is good.
Not sure if it was mentioned but you can switch the 1st 2 small tubes to see if the dead channel comes to life, (and the other one goes silent from a bad tube.)
If it says "Vintage" on it, -it isn't.
Re: 1966 Bandmaster Blues
what's a pop test? (sorry for maybe a stupid question...again)billyz wrote:
The signal probe setup is a very good tool. I usually just do a POP test.
thanks
Re: 1966 Bandmaster Blues
Did that, but without succes.jjman wrote: Not sure if it was mentioned but you can switch the 1st 2 small tubes to see if the dead channel comes to life, (and the other one goes silent from a bad tube.)
not sure if I have time to work on this amp this week.
But I'll keep in touch.
Thank you.
Re: 1966 Bandmaster Blues
The Pop test is a quick simple test to help you determine the part of the circuit which is not passing the signal. Basically you you begin by using a Volt meter( set to measure DC Volts) to probe the circuit AND LISTEN for the POP noise it makes( through the amps Speaker) when touching the circuit . For example, you would start at the power tubes, you will hear a small pop through the speaker, as you progress to the Phase Invertor stage the pop will be louder. Again the preamp stages will will be louder still. If at one stage you fail to hear a POP , that will most likely be the part of the circuit that has failed.
So you might want to start at your first preamp tube and test the pins 1 (plate v1a) pin 2 (input grid v1a) and pin 6 (v1b plate) and pin 7 (v1b grid).
If you can hear the POP , most likely your problem is before these test points, like the input jack. If no POP it is after or right there. This does not work on every part of the circuit. The more you poke around the better you'll get at it.
This assumes you have already verified the later parts of the circuit. I believe you said only channel one is dead.
So you might want to start at your first preamp tube and test the pins 1 (plate v1a) pin 2 (input grid v1a) and pin 6 (v1b plate) and pin 7 (v1b grid).
If you can hear the POP , most likely your problem is before these test points, like the input jack. If no POP it is after or right there. This does not work on every part of the circuit. The more you poke around the better you'll get at it.
This assumes you have already verified the later parts of the circuit. I believe you said only channel one is dead.
Re: 1966 Bandmaster Blues
Yeah, only channel one is dead.billyz wrote:The Pop test is a quick simple test to help you determine the part of the circuit which is not passing the signal. Basically you you begin by using a Volt meter( set to measure DC Volts) to probe the circuit AND LISTEN for the POP noise it makes( through the amps Speaker) when touching the circuit . For example, you would start at the power tubes, you will hear a small pop through the speaker, as you progress to the Phase Invertor stage the pop will be louder. Again the preamp stages will will be louder still. If at one stage you fail to hear a POP , that will most likely be the part of the circuit that has failed.
So you might want to start at your first preamp tube and test the pins 1 (plate v1a) pin 2 (input grid v1a) and pin 6 (v1b plate) and pin 7 (v1b grid).
If you can hear the POP , most likely your problem is before these test points, like the input jack. If no POP it is after or right there. This does not work on every part of the circuit. The more you poke around the better you'll get at it.
This assumes you have already verified the later parts of the circuit. I believe you said only channel one is dead.
I'm off, I need to poke around.
Re: 1966 Bandmaster Blues
Ok, just poked around a bit.
On V1: Pin 1 (plate) small pop. Pin2 nothing. Pin6 (plate) pop! Pin 7 (grid) nothing.
On V1: Pin 1 (plate) small pop. Pin2 nothing. Pin6 (plate) pop! Pin 7 (grid) nothing.
Re: 1966 Bandmaster Blues
Measure the cathode voltage on pins 3 and 8 should be around 2.0 volts.
Re: 1966 Bandmaster Blues
V1 pin 3 = 2,02Vbillyz wrote:Measure the cathode voltage on pins 3 and 8 should be around 2.0 volts.
V1 pin 8 = 2,29V
V1 pin 3 = 2,5V
V1 pin 8 = 2,30V
Thanks