Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: concertamp64 on September 06, 2020, 08:49:10 pm

Title: Fender Service Parts List 1
Post by: concertamp64 on September 06, 2020, 08:49:10 pm: Just finished installing the caps and resistors in the Hoffman 'Fender Service Parts List 1' kit on my 64 Fender Concert. I visually checked, rechecked...rechecked again......what's best way to proceed at this point?......any tests I should perform before powering on?....as you can tell I'm new at this....any comments will be greatly appreciated...
Title: Re: Fender Service Parts List 1
Post by: sluckey on September 06, 2020, 09:59:37 pm: What was the state of the amp before you replaced all those caps and resistors?
Title: Re: Fender Service Parts List 1
Post by: Latole on September 07, 2020, 03:55:24 am: 1- Remove Power tubes, Power amp ON and read how much negative bias voltage you read on pin 5 ( you should have close to -30 vdc if I'm right, less than -25 vdc check bias circuit)

2- I often use bulb current limiter too. to protect amp in case of short circuit
3- Check if amp have the right fuse
Title: Re: Fender Service Parts List 1
Post by: Latole on September 07, 2020, 03:56:28 am: Quote from: sluckey on September 06, 2020, 09:59:37 pm
What was the state of the amp before you replaced all those caps and resistors?

100 % right.
Title: Re: Fender Service Parts List 1
Post by: concertamp64 on September 07, 2020, 09:25:47 am: Thanks for replying.....The amp had all original caps and resistors. Power tubes and 1 or 2 preamp tubes were replaced though the years. It really had no issues....other than to me just didn't sound good any more. The large caps all had blisters.....I am the original owner...bought it new in 1964 in El Dorado Ark.
Title: Re: Fender Service Parts List 1
Post by: PRR on September 07, 2020, 02:03:53 pm: I would suggest a Lamp Limiter just in case there is a wiring or part fault. But basically it "should work".
Title: Re: Fender Service Parts List 1
Post by: Latole on September 07, 2020, 02:10:50 pm: For good tune-up: Use good contact cleaner on each pot and on tubes's socket, slide tubes few time to clean.
Title: Re: Fender Service Parts List 1
Post by: concertamp64 on September 08, 2020, 06:47:22 am: thanks for the replies......I'm building the light bulb current limiter........which wattage light bulb?....internet is all over the place on this question...some say lower wattage offers more protection...others say higher / 250 watts etc. offers more protection....
Title: Re: Fender Service Parts List 1
Post by: sluckey on September 08, 2020, 06:53:50 am: I would use a 60 watt bulb for a 2 x 6L6 amp.
Title: Re: Fender Service Parts List 1
Post by: EL34 on September 08, 2020, 07:11:51 am: Follow my Fender service guide here
https://el34world.com/schematics.htm#Servicing%20fender%20amps (https://el34world.com/schematics.htm#Servicing%20fender%20amps)
Title: Re: Fender Service Parts List 1
Post by: concertamp64 on November 13, 2020, 04:18:54 pm: Got through amp power up with lightbulb limiter ok with no issues.....now need to tackle the bad brittle like tone...I thought the new caps might help...but didn't