Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: SMSgtCC on May 09, 2024, 08:37:08 pm

Title: Fender Deluxe Reverb Mojo Tone kit Channel 2 problem
Post by: SMSgtCC on May 09, 2024, 08:37:08 pm: Just completed build of Deluxe Reverb - Mojo Tone kit.

Normal channel loud, treble and bas respond nicely.

Vibrato channel: Weak output, no reverb or vibrato.

So far, swapped all the small tubes (12AX7 and the two 12AT7's). Verified connections and solder joints to tube sockets, jacks on back of chassis, and on back of pots and board.

What can I try next?

Thanks.
Title: Re: Fender Deluxe Reverb Mojo Tone kit Channel 2 problem
Post by: passaloutre on May 09, 2024, 10:06:17 pm: Do you have a signal generator and a listening probe?
Title: Re: Fender Deluxe Reverb Mojo Tone kit Channel 2 problem
Post by: SMSgtCC on May 09, 2024, 10:17:41 pm: I'll take voltage readings at pins on each tube socket and repost tomorrow - thanks.
Title: Re: Fender Deluxe Reverb Mojo Tone kit Channel 2 problem
Post by: SMSgtCC on May 09, 2024, 10:18:52 pm: No - I don't have either of those.
Title: Re: Fender Deluxe Reverb Mojo Tone kit Channel 2 problem
Post by: passaloutre on May 09, 2024, 10:34:40 pm: You can make a probe with some wire and a capacitor, and you can use a smartphone as a signal generator. These tools help you find where you’re losing the signal.
Title: Re: Fender Deluxe Reverb Mojo Tone kit Channel 2 problem
Post by: SMSgtCC on May 09, 2024, 11:17:44 pm: That's sounds very useful. I will look into that - thanks!
Title: Re: Fender Deluxe Reverb Mojo Tone kit Channel 2 problem
Post by: SMSgtCC on May 10, 2024, 07:12:42 am: Voltage Readings: 5/10/24 05:45 AM

   Pin: Voltage
V1   1: 190
   3: 1.43
   6: 196.6
   8: 1.46

V2   1: 184.8
   3: 1.40
   6: 184.7
   8: 1.46

V3   1: 414.0
   3: 7.412
   6: 184.7
   8: 1.46

V4   1: 189.3
   3: 1.58
   6: 191.2
   8: 1.57

V5   1: 409.4
   3: .1 mV
   6: 360
   8: .5 mV

V6   1: 198
   3: 70.4
   6: 198
   8: 70.4

*V5 measurements don’t agree with schematic except for pin 6.
Title: Re: Fender Deluxe Reverb Mojo Tone kit Channel 2 problem
Post by: tdvt on May 10, 2024, 07:28:16 am: Just for reference, assuming THIS (https://www.mojotone.com/Amp_Kits/Blackface/Deluxe_Reverb_SCH.pdf?_gl=1*p5h7g2*_gcl_au*MTgyNjA2MTIxMy4xNzEzNzQ4MDU3LjE3MjM0NzE0NTYuMTcxNTM0MjU3Ni4xNzE1MzQyNTkw*_ga*NDIwNjI5MjkyLjE2OTgwMTE0ODg.*_ga_82F088JBDD*MTcxNTI5MDI5NS45Ny4xLjE3MTUzNDM3OTUuNDkuMC4w) one..
Title: Re: Fender Deluxe Reverb Mojo Tone kit Channel 2 problem
Post by: SMSgtCC on May 10, 2024, 07:31:38 am: Yes - I believe so. The kit came with revision 5 of this schematic.
Title: Re: Fender Deluxe Reverb Mojo Tone kit Channel 2 problem
Post by: SMSgtCC on May 10, 2024, 07:56:52 am: Found it. Yellow wire ("Y" on original layout) that connects to .1 cap - other side of this cap connects to pin 6 on V4 - that wire had come lose - bad solder joint underneath board. Thanks everyone!
Title: Re: Fender Deluxe Reverb Mojo Tone kit Channel 2 problem
Post by: sluckey on May 10, 2024, 08:12:17 am: Quote from: SMSgtCC on May 10, 2024, 07:12:42 am
Voltage Readings: 5/10/24 05:45 AM
V5 reading are OK. Both triodes are in hard cutoff because there is no footswitch connected. You can enable the tremolo by grounding the tip of the FS jack. Then voltages will look much different and the tremolo will work.

V3 is a concern. Pins 1, 6 are jumped together and should have the same voltage. Pins 2, 7 are jumped together and should have the same voltage. Pins 3, 8 are jumped together and should have the same voltage. Your different voltages indicate you did not put the three jumpers on the socket. (This is not causing the weak vibrato channel)

Show us some hi-rez pics. Resolution should be good enough to clearly read resistor values.
Title: Re: Fender Deluxe Reverb Mojo Tone kit Channel 2 problem
Post by: SMSgtCC on May 10, 2024, 08:17:58 am: Found it. Yellow wire ("Y" on original layout) that connects to .1 cap - other side of this cap connects to pin 6 on V4 - that wire had come lose - bad solder joint underneath board. Thanks everyone!
Title: Re: Fender Deluxe Reverb Mojo Tone kit Channel 2 problem
Post by: stratomaster on May 10, 2024, 05:28:51 pm: You still need to chase down Sluckey's observation above. Your reverb driver is not where it should be.