Mojotone Amp Kits Leave A Lot To Be Desired........................
- Thread starter Jeffblue
- Start date
Jeffblue
Well-known member
Re: Mojotone Amp Kits Leave A Lot To Be Desired........................
Scott, I was missing a 220k ohm 1/2 watt resistor in my kit and in my stash of parts I had a 220 k ohm 1 watt resistor that I used in it's place on pins 3 & 8 on the output tube socket. Would the difference in wattage be an issue?
Scott, I was missing a 220k ohm 1/2 watt resistor in my kit and in my stash of parts I had a 220 k ohm 1 watt resistor that I used in it's place on pins 3 & 8 on the output tube socket. Would the difference in wattage be an issue?
Jeffblue
Well-known member
Re: Mojotone Amp Kits Leave A Lot To Be Desired........................
Voltage on pin 1 & 6 on the output tube socket is 353 Volts DC.
Voltage on pin 1 & 6 on the output tube socket is 353 Volts DC.
crusty philtrum
Vintageologist
Re: Mojotone Amp Kits Leave A Lot To Be Desired........................
Not Scott.
1 Watt resistors are almost always preferable to 1/2 Watt equivalents in valve amps. I never use 1/2 Watt resistors.
(One of many reasons I'd never buy a kit).
Not Scott.
1 Watt resistors are almost always preferable to 1/2 Watt equivalents in valve amps. I never use 1/2 Watt resistors.
(One of many reasons I'd never buy a kit).
Re: Mojotone Amp Kits Leave A Lot To Be Desired........................
Not Scott either. But no, 1 watt is fine. Wont make a difference.
Not Scott either. But no, 1 watt is fine. Wont make a difference.
Re: Mojotone Amp Kits Leave A Lot To Be Desired........................
You said V1 wasn't glowing as bright. Some tubes don't but you should check the voltages on V1. Check filament voltage (pin 4/5 to pin 9). Should be in the 6.3 volt range with tube in socket. And check V1 plates (pins 1 and 6) as Scott suggested.
You said V1 wasn't glowing as bright. Some tubes don't but you should check the voltages on V1. Check filament voltage (pin 4/5 to pin 9). Should be in the 6.3 volt range with tube in socket. And check V1 plates (pins 1 and 6) as Scott suggested.
Jeffblue
Well-known member
Re: Mojotone Amp Kits Leave A Lot To Be Desired........................
I was having difficulty with the volume of the amp and the 12AY7 preamp tube was burning dimly. I changed the 12AY7 for an NOS 6072 and the effects were immediate. The 6072 tube is burning brightly and the volume is now at an acceptable level. Bad preamp tube.
I was having difficulty with the volume of the amp and the 12AY7 preamp tube was burning dimly. I changed the 12AY7 for an NOS 6072 and the effects were immediate. The 6072 tube is burning brightly and the volume is now at an acceptable level. Bad preamp tube.
Re: Mojotone Amp Kits Leave A Lot To Be Desired........................
Have you used a shielded cable from what I'm guessing is the volume pot to pin 2 or 7 depending on the circuit? That will cut noise. Only ground one end of it or you'll create a ground loop.
Have you used a shielded cable from what I'm guessing is the volume pot to pin 2 or 7 depending on the circuit? That will cut noise. Only ground one end of it or you'll create a ground loop.
Jeffblue
Well-known member
Re: Mojotone Amp Kits Leave A Lot To Be Desired........................
I fired up the amp this morning and I had good tone and enough volume on channel 2. I then switched to channel 1 and I could barely hear any sound. I switched back to channel 2 and the sound immediately dropped. I then removed the tubes and flipped the chassis to test voltages. All of the plate voltages on all tube sockets pins 1 & 6 were all approximately 340 volts DC. All the filament voltages on pins 4,5 & 9 were all reading 6.4 volts AC. Any ideas what to check next?
I fired up the amp this morning and I had good tone and enough volume on channel 2. I then switched to channel 1 and I could barely hear any sound. I switched back to channel 2 and the sound immediately dropped. I then removed the tubes and flipped the chassis to test voltages. All of the plate voltages on all tube sockets pins 1 & 6 were all approximately 340 volts DC. All the filament voltages on pins 4,5 & 9 were all reading 6.4 volts AC. Any ideas what to check next?
Re: Mojotone Amp Kits Leave A Lot To Be Desired........................
Possible cold solder joint/joints. Poke around with a "chopstick" (non conductive probe) if nothing looks obvious. Amp on, plugged up, keep your free hand out of the chassis. Listening for crackling or volume increase/decrease. Focus on all solder joints but I'd start with tube sockets. Resistors as well. Also, have seen broken wire inside the insulation from scoring the wire when removing the jacket, but that's usually with solid core wire.
Possible cold solder joint/joints. Poke around with a "chopstick" (non conductive probe) if nothing looks obvious. Amp on, plugged up, keep your free hand out of the chassis. Listening for crackling or volume increase/decrease. Focus on all solder joints but I'd start with tube sockets. Resistors as well. Also, have seen broken wire inside the insulation from scoring the wire when removing the jacket, but that's usually with solid core wire.
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Mojotone Amp Kits Leave A Lot To Be Desired........................
Tap the solder joints with the wooden chop stick. It will become obvious. Have patience. Also if you want to scan the layout sheet and send it to me, I'll try and help you trouble shoot. scott@celticamps.com
(Do both channels share V1?)
Tap the solder joints with the wooden chop stick. It will become obvious. Have patience. Also if you want to scan the layout sheet and send it to me, I'll try and help you trouble shoot. scott@celticamps.com
(Do both channels share V1?)
Jeffblue
Well-known member
Re: Mojotone Amp Kits Leave A Lot To Be Desired........................
Both channels do not share V1. I believe I have a problem with the rectifier cap. I am reading over 300 volts DC on the pin of the cap going to the output transformer and the plates of both triodes on the output tube, but the remaining pins and the plates of all of the other tubes are reading 6 volts DC. All of the filaments are reading the appropriate 6.3 volts AC.
Both channels do not share V1. I believe I have a problem with the rectifier cap. I am reading over 300 volts DC on the pin of the cap going to the output transformer and the plates of both triodes on the output tube, but the remaining pins and the plates of all of the other tubes are reading 6 volts DC. All of the filaments are reading the appropriate 6.3 volts AC.
