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Post subject: Ancient tubes
Posted: Sat Sep 10, 2011 6:26 am
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I have a '60's Gibson Hawk amp - very much like a Princeton Reverb. The Gibson is completely original except for the speaker that had literally fallen apart (I put in the same Jensen that the PRRI has). Anyways, it has a very sweet, clean sound and great reverb and tremolo. Would replacing the 45 year old tubes make it sound a lot better. BTW, the tubes are from the Lowery organ company which I guess makes sense since both Lowery and Gibson were owned by the same company back then.


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Post subject: Re: Ancient tubes
Posted: Sat Sep 10, 2011 6:42 am
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Depends on if the tube are worn out. If the amp been in steady use over these 40+ years it prolly would not hurt to roll a set of new tubes and check the power tube idle bias.

I'd think RI Mullard ECC83/12AX7 and Sovtek EL84M (same as Reflector 6N14P-EV, be sure to get the -EV or mil spec version) would be a nice combo. Check the 100 watt resistor shared by the cathodes of the 6BQ5 (EL84) and tied to ground, for drifting (10-15% or more = replace). And replace the 100 mfd electrolytic cap paralleling this resistor with a new Sprague ATOM (or some similar quality cap) with at least 100 VDC rating.

I believe this amp has a 40/20/20 450 VDC cap can in it power supply. AES stocks these. Prolly a good idea to replace it.

Good luck with this amp. Gibson made some pretty sweet amps in those days.

http://www.gibson.com/Files/schematics/Hawk.PDF


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Post subject: Re: Ancient tubes
Posted: Sat Sep 10, 2011 7:40 am
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BMW2002Ti wrote:
Depends on if the tube are worn out. If the amp been in steady use over these 40+ years it prolly would not hurt to roll a set of new tubes and check the power tube idle bias.

I'd think RI Mullard ECC83/12AX7 and Sovtek EL84M (same as Reflector 6N14P-EV, be sure to get the -EV or mil spec version) would be a nice combo. Check the 100 watt resistor shared by the cathodes of the 6BQ5 (EL84) and tied to ground, for drifting (10-15% or more = replace). And replace the 100 mfd electrolytic cap paralleling this resistor with a new Sprague ATOM (or some similar quality cap) with at least 100 VDC rating.

I believe this amp has a 40/20/20 450 VDC cap can in it power supply. AES stocks these. Prolly a good idea to replace it.

Good luck with this amp. Gibson made some pretty sweet amps in those days.

http://www.gibson.com/Files/schematics/Hawk.PDF


+1

You might give some consideration to having the original speaker re-coned. Frequently these were CTS alnico's which are some of the sweetest-sounding OEM drivers.

Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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