Bogen H-30 guitar mod - diyAudio
Go Back   Home > Forums > Live Sound > Instruments and Amps
Home Forums Rules Articles diyAudio Store Gallery Wiki Blogs Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Instruments and Amps Everything that makes music, Especially including instrument amps.

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
Thread Tools Search this Thread
Old 12th April 2007, 06:47 AM   #1
diyAudio Member
Join Date: Apr 2007
Question Bogen H-30 guitar mod

This is my first tube amp project and I'm a chemistry major not an EE so bear with me here...

So I picked up this Bogen H-30 from the local thrift store for $1.98 (yes, the decimal is in the right place).
It's got three 6sf5's for the preamps (mic1, mic2, phono), a 6sl7 PI, two 6l6's OP, and a 5u4 rectifier. The circuitry of the phase inverter, output stage and tone control is still a little over my head (hell, three weeks ago I didn't even know what a phase inverter was!), so hopefully someone can help me out...

Thus far, I've added my 1/4" jack and connected the output of the first microphone stage to the grid of the second mic stage. I am already in love with the distortion those octal preamp tubes produce, however, the frequency response is all wrong.

I'd like to modify the tone control to be more responsive to the guitar frequency range. The amp has a 6-position knob with filters ranging from natural, mellow, bass, deep bass, bright, and crisp. The only two remotely suitable for the guitar are 'bright' and 'crisp.' I would like to retain the 6-position switch but using RC combinations appropriate for guitar amplification (i.e. 6 different hardwired bass, middle, treble configurations). Could someone please help me with this? Any other comments/suggestions are welcome as well.


I've attached a copy of the schematic. Big thanks to 'ivegotthat' on ebay for working with me to find it.
  Reply With Quote
Old 13th April 2007, 07:15 AM   #2
diyAudio Member
aletheian's Avatar
Join Date: Apr 2004
Location: Philly
Default Re: Bogen H-30 guitar mod

Originally posted by tgrizzle

I've attached a copy of the schematic.

um... where is the schematic?
Heghlu'meH QaQ jajvam!
  Reply With Quote
Old 13th April 2007, 08:17 PM   #3
diyAudio Member
Join Date: Apr 2007
errr... I thought I did anyway..

try that:
  Reply With Quote
Old 13th April 2007, 10:45 PM   #4
Tweeker is offline Tweeker  United States
diyAudio Member
Join Date: Dec 2004
Location: Cincinnati, Ohio
This tool may be of some help to you.
Be sure your foil hat has a good low impedance ground.
  Reply With Quote
Old 14th April 2007, 02:47 AM   #5
diyAudio Member
Join Date: Feb 2002
Location: Western Sydney
That tone control is in the feedback network, unlike most guitar tone 'stacks'. The closest thing is the presence control in a Marshall or Fender.

Usually, guitar amp tone controls are passive, and cause quite a bit of signal loss, so you might need the extra gain of the first stage if you put one in. Look at how trad guitar preamps are wired.

If you're new to this, just remember....the voltages in there can KILL YOU,... know exactly what you're doing before you jump in...
Pete McK
  Reply With Quote
Old 14th April 2007, 10:50 PM   #6
diyAudio Member
Join Date: Apr 2007
Thank you kindly for the responses!

Again, I apologize for my n00bishness; however yes sir, I am quite aware of the dangers associated with electricity inside this amp.

Yes, I figured something hairy was going on with that tone switch being connected to the output transformer like that.
So could I replace R20 with a 220k pot wired up with the resistor and capacitor of position 6 (crisp) and call it 'presence?' Playing through the amp on this setting does in fact sound like playing through a guitar amp with the presence cranked.

Is the best place for my tone stack right before the decoupling (?) capacitor, C8? I still want to use the 6-position switch for this. Could I simply take the tone stack circuit for, say a Marshall, and replace the pots with different value resistances to acheive the hard-wired filters?

  Reply With Quote


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
bogen mx-60a tube pa amp guitar ElectricMan Swap Meet 1 3rd May 2009 02:02 AM
Bogen J130 PA to guitar amp? bigaldo Instruments and Amps 0 18th February 2008 04:36 AM
Bogen K15 convert to guitar amp tonemonster Instruments and Amps 0 29th March 2007 08:11 PM
Ancient Bogen 807PP Amp-Guitar Trout Instruments and Amps 0 5th May 2006 11:14 PM
Bogen PA to Guitar Amp, few questions Turbo7MN Instruments and Amps 100 5th April 2006 01:41 AM

New To Site? Need Help?

All times are GMT. The time now is 02:30 PM.

vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Copyright 1999-2017 diyAudio

Content Relevant URLs by vBSEO 3.3.2