Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: kagliostro on January 13, 2017, 01:30:57 pm

Title: Gibson GA80 Varitone .... B+ and Power ?? [WRONG Post don't waste time reading]
Post by: kagliostro on January 13, 2017, 01:30:57 pm

This is the GA80 Varitone schematic

(http://i.imgur.com/NUdbXOX.jpg)

and here a link where you can read a description of the amp

https://www.vintageguitar.com/16351/gibson-ga-80t-vari-tone/ (https://www.vintageguitar.com/16351/gibson-ga-80t-vari-tone/)

on the link you can read

Quote

Circa-1960 Gibson GA-80T Vari-Tone.
• Preamp tubes: two 12AX7, two 5879
• Output tubes: two 6L6
• Rectifier: GZ34
• Controls: Ch1: Volume, Tone; Ch2: Volume, Tone, six Vari-Tone Selector pushbuttons, tremolo Depth and Frequency
• Speakers: one 15″ Jensen P15P alnico speaker
• Output: approximately 25 watts RMS

and I'm in doubt about, because on the Voltage Table on the schematic you can read 350V AC and 438V B+

the Application Data of the 6L6GB is this

(http://i.imgur.com/KTuVURA.jpg)

I can read 24W of output with B+ 360v - G2 270v - Rk 250R - Load 9K

Any idea about this ?

Is possible that B+ is so high on the schematic (438v), which can be the power and the OT primary impedance ???

Thanks

Franco

Title: Re: Gibson GA80 Varitone .... B+ and Power ??
Post by: VMS on January 13, 2017, 02:20:25 pm

I believe voltage table says 420v plate voltage and 30V cathode so that makes 390V plate to cathode voltage.


Also i don't think this is a 'class A' amplifier.

Title: Re: Gibson GA80 Varitone .... B+ and Power ??
Post by: VMS on January 13, 2017, 02:21:33 pm

http://el34world.com/Forum/index.php?topic=18608.0 (http://el34world.com/Forum/index.php?topic=18608.0)

Title: Re: Gibson GA80 Varitone .... B+ and Power ??
Post by: kagliostro on January 13, 2017, 02:37:01 pm

Really, my mind is doing bad things :BangHead: :BangHead: :BangHead:


Thanks VMS


Franco

Title: Re: Gibson GA80 Varitone .... B+ and Power ??
Post by: VMS on January 13, 2017, 02:46:42 pm

Don't worry, you are not alone.


I often start to ask something and after little search find that i have asked the very same question few years earlier. 


I didn't remember that thread either, I was google searhing ga80 primary impedance.

Title: Re: Gibson GA80 Varitone .... B+ and Power ??
Post by: kagliostro on January 13, 2017, 04:34:05 pm

Sorry

 :dontknow: :dontknow:


Franco