1959 Pilot AA-908 Amp into Guitar Amp - diyAudio
Go Back   Home > Forums > Amplifiers > Tubes / Valves

Tubes / Valves All about our sweet vacuum tubes :) Threads about Musical Instrument Amps of all kinds should be in the Instruments & Amps forum

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 16th March 2008, 10:58 PM   #1
aronaut is offline aronaut  United States
diyAudio Member
 
Join Date: Mar 2008
Default 1959 Pilot AA-908 Amp into Guitar Amp

Hello all,
I came across this thread http://www.diyaudio.com/forums/showt...?postid=389321 and realized I could do the same thing with an old Pilot monoblock amp I have kicking around.

I have hosted the schematic and a couple pics of it here: http://www.zeromassstudio.com/pilot.html

I'm hoping to alter the preamp stages to a Fender 5F6-A type (or similar, if I can get away with using as much as what's currently in the Pilot that would be great) but not sure it will be possible using the current transformer combination (they're huge!) it says the output is 40W which should be great for a guitar amp. I tried a guitar through it and it sounds interesting a little low volume right now and muffled but I think that's due to the gain stage and negative feedback.

Any help I could get with this would be great, Iv'e been wanting to try my hand at a tube guitar amp (5F6-A clone) and figured this would be a great way to start.

Thanks

Aron
  Reply With Quote
Old 17th March 2008, 07:06 AM   #2
diyAudio Member
 
Join Date: Jan 2002
Location: nowhere
Indeed that amp can be a very good guitaramp.
One clue when it comes to EQ'ing a circuit for electric guitar is to get it brightened up. 'So bright it hurts' one bluesman told me, and it is true since a flat EQ sounds very muffled and dull.
Gainwise you can get very good clean tones, with a nice hint of breakup with a single 12ax7 gainstage, but you must remove all feedback, also the 'AC balance'.
Also, when the input impedance is low like here, you get a muffled tone from the pickups, 1megohm will help brighten it up.
For a basic gainstage with 12ax7 try this for starters: 1kohm cathoderesistor bypassed with 1uF, 220kohm plateresistor, 10nF couplingcap to phasesplitter. You can switch in more coupling caps for a deeper (jazzier) tone.
A volumecontrol should be placed after the gainstage, or simply use the guitarvolume.
I would keep this amp simple, and use various effects pedals to very the tone/gain/overdrive.
  Reply With Quote
Old 18th March 2008, 07:32 AM   #3
aronaut is offline aronaut  United States
diyAudio Member
 
Join Date: Mar 2008
Thanks Semper Fi, I've been able to get the guitar input sounding pretty good just by omitting the feedback to the first gain stage and adding 1m impedance. I also ommited the AC Balance half of the 1st 12AX7, with little change. However I'm having trouble with hum, and am confused with the phase inversion as it appears on this schematic. I tried ommiting the AC balance pot which was fine, then the DC balance pot which got rid of the hum but made the input sound like crap, I'm assuming this is part of the phase inverter and should remain, but comparing to a long tailed phase inverter (ala 5F6-A) I'm confused. I think next I'll just copy the 5F6-A inverter using the same 12AX7, but still not sure if it will fix the hummm...
what do you think?

Thanks!
  Reply With Quote
Old 18th March 2008, 09:08 AM   #4
diyAudio Member
 
Join Date: Jan 2002
Location: nowhere
A closer look and I see the AC Balance is part of the phase inverter's actual phase inverting, so my bad, untill you build the phase inverter you mention, which I agree is a better type, you need to reaply the AC Balance connection.
You probably get som opposing powersupply ripple in that way as well, which helps with reducing the hum.
  Reply With Quote
Old 18th March 2008, 03:58 PM   #5
kevinkr is offline kevinkr  United States
diyAudio Moderator
 
kevinkr's Avatar
 
Join Date: Sep 2004
Location: Boston, Massachusetts
Blog Entries: 6
These amplifiers are comparatively rare, and had very good quality iron, and they're collectible. Rather than repurpose it I would recommend trying to sell it as is, and apply the proceeds to building a new guitar amplifier from the ground up.
__________________
"Extraordinary claims require extraordinary evidence." - Carl Sagan
  Reply With Quote
Old 18th March 2008, 11:09 PM   #6
aronaut is offline aronaut  United States
diyAudio Member
 
Join Date: Mar 2008
What do you think one of these could go for? I couldn't find one on ebay...
  Reply With Quote
Old 19th March 2008, 08:38 AM   #7
aronaut is offline aronaut  United States
diyAudio Member
 
Join Date: Mar 2008
So I replaced the inverter with the 5F6A type and it took care of the hum, but now the guitar breaks up in a really ugly way, similar to the way it sounded with the original circuit without the DC balance pot. It sounded really nice and Fender-like with the original inverter - just noisy. I might go back to the original inverter and try to track down the noise elsewhere. Any suggestions?

...I guess if all else fails I can bring the whole thing back to original and sell it as kevinkr suggested.
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Pilot LED for my new car Amplifier raghs Car Audio 11 27th March 2009 05:03 PM
bias pilot sa 260 baltimoreblues Tubes / Valves 0 17th February 2008 08:55 PM
Pilot SA 260 bias baltimoreblues Tubes / Valves 1 3rd February 2008 06:00 PM
Video with 1959 audiophile (in swedish) Christer Everything Else 3 31st December 2006 12:37 AM
pilot 264 jaron Tubes / Valves 17 13th March 2006 03:32 PM


New To Site? Need Help?

All times are GMT. The time now is 12:31 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2