Recent Posts

61

Tube Amp Building - Tweaks - Repairs / 1968 Fender Vibrochamp AA764 Resto

« Last post by TIMBO on December 06, 2025, 04:22:29 am »

Hey guys,
I have the pleasure to restore one of these.
 











I'll be looking for some guidance on how much I'll need to remove and replace to keep it as original and safe to use

62

Tube Amp Building - Tweaks - Repairs / Re: 5879 Blues Bassman

« Last post by TIMBO on December 06, 2025, 02:45:55 am »

Hey guys,
This one fired up well.

63

Tube Amp Building - Tweaks - Repairs / Re: Carvin Legacy 3 bias issue or design?

« Last post by EddyMunster on December 05, 2025, 10:16:38 pm »

Just a quick update. The new r55 3watt resistor is already a little discolored after playing the amp for a couple of weeks.   Found some 5 watt ceramic resistors to put in its place on both amps. Got one of the amps up for sale on Reverb. I ended up liking 111mA bias best for these amps. All is good now and sounds great!

Cheers

64

Tube Amp Building - Tweaks - Repairs / Re: Please do not use VPN's

« Last post by tubeswell on December 05, 2025, 09:06:33 pm »

to “be outside” the UK.

 
we're watching the beginning of the end of "internet www" I watched in horror as www took over FTP, I could spend days reading white-papers from MIT, Cal-Tech....www offered to sell me access for $19.99 a month, Web-AI will want your kidney, maybe your soul for access
 

Yes this has me worried too. Next thing they’ll take over the International Date Line, and bang goes yesterday and tomorrow…

65

Tube Amp Building - Tweaks - Repairs / Re: Fender Vibro-Champ w/o vibro build - OT hook up & review please

« Last post by dogburn on December 05, 2025, 07:25:58 pm »

I just used the standard resistor for NFB and added a switch to cut it out of the circuit. You could do a three-way switch with two different resistor values plus cutting it out, but I haven't found that as useful as a simple NFB/no NFB switch.

66

Tube Amp Building - Tweaks - Repairs / Re: Fender Vibro-Champ w/o vibro build - OT hook up & review please

« Last post by RoadShow on December 05, 2025, 06:19:29 pm »

Updated schematic...

67

Tube Amp Building - Tweaks - Repairs / Re: Please do not use VPN's

« Last post by shooter on December 05, 2025, 05:16:27 pm »

to “be outside” the UK.

 
we're watching the beginning of the end of "internet www" I watched in horror as www took over FTP, I could spend days reading white-papers from MIT, Cal-Tech....www offered to sell me access for $19.99 a month, Web-AI will want your kidney, maybe your soul for access
 

68

Tube Amp Building - Tweaks - Repairs / Re: Please do not use VPN's

« Last post by tristanc on December 05, 2025, 04:47:14 pm »

I doubt any of that will happen.
You should be able to access the forum without using a VPN

Access the forum, yes. Viewing any image posted using imgur, no. The work round is to use a VPN, even temporarily, to “be outside” the UK.

edited to add an example

69

Tube Amp Building - Tweaks - Repairs / Re: Testing Bad Filter Cap with a scope for 120HZ hum

« Last post by wsscott on December 05, 2025, 04:23:19 pm »

The jack is isolated.  Do you want me just to take the jack’s ground lug out of the circuit by un-wiring it?

70

Tube Amp Building - Tweaks - Repairs / Re: Fender Vibro-Champ w/o vibro build - OT hook up & review please

« Last post by RoadShow on December 05, 2025, 03:41:16 pm »

Yep, that transformer works, but you also might consider the Hammond 1760CP, which has a 4 Ohm tap rather than 3.2 Ohm, since new 3.2 Ohm speakers aren't common (but it's a minor difference anyway).

I built a no-trem Champ (the AA764, as exnihilfit pointed out), and added a NFB switch, which is a really useful mod if you are looking for additional tweaks to the circuit. I also add a mid/raw pot (from Rob Robinette's site) to give more tonal flexibility that can send the sound into more tweed territory.

1760CP, yes, but the 1760C has 8 & 16 ohm options, CP doesn't have 16.

What resistors did you use for NFB switch?  For the AB763 example he uses 820/1.5k whereas the Champ starts with 2.7k.

Thanks