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Ashdown LB30 schematic


JapanAxe
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33 minutes ago, Twincam said:

May I ask what's the project? 

You may!

I have just acquired (as scrap) a Carvin Vintage 33 combo. The cabinet is more than a little distressed, the speaker is blown, but both transformers work. My plan is to take the existing chassis and transformers (and some other useful working parts e.g. switches, pilot light) and convert it to a 30W bass head with the following features:

  • Output section based around four EL84 valves, because that's what the OT is suited for - hence my interest in the LB30 schematic;
  • Preamp based on a 1964 Amped B15 channel;
  • That's about it!

I need to make sure that the pre-amp will work with the power amp (i.e. that phase splitter has enough beans to drive all the EL84s), so I will be working on my understanding of push-pull amps and hitting up the forums .

Here's the innards as I got the amp, and the almost-gutted chassis:

ncWLml2.jpga1QSlUL.jpg

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Just had a quick look at that schematic.

  • The PI/driver is a 12AU7, and it will probably be simplest if I keep that in and follow the circuit from the wiper of the volume pot - before that will be my 6SL7-based B15-style pre-amp.
  • Solid state rectifier for the HT - works for me, as I have no 5V secondary on my PT, and there is enough power available on the 6V heater secondary for four EL84s and four 12AX7s.
  • Am I right in thinking that is cathode biased like an AC30?
23 minutes ago, Twincam said:

Excellent! So will there be a thread on this. I would be very interested to see how this turns out. 

 

Yes there will, but first there will be a design-based thread in the Repairs & Technical forum, and in the Tube Amp DIY Builders Facebook group to which I subscribe (where you get people like Rob Robinette and Bruce Egnater chipping in with advice!)

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Sounds a fun project, if you give us a call and chat to Dave Green(who designed the LB30)he will more than likely give you some advice(he normally does even when not asked...) on how to tie everything up... I’m fairly sure he won’t mind you being ‘inspired’ by his output stage... but sometimes he can be a tad grumpy so you takes your chances 😉 

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8 minutes ago, Ashdown Engineering said:

Sounds a fun project, if you give us a call and chat to Dave Green(who designed the LB30)he will more than likely give you some advice(he normally does even when not asked...) on how to tie everything up... I’m fairly sure he won’t mind you being ‘inspired’ by his output stage... but sometimes he can be a tad grumpy so you takes your chances 😉 

Thanks! Another option was the AC30 output stage - I found the schematic for the 'bass' version on the Dr Tube website.

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14 hours ago, Ashdown Engineering said:

Sounds a fun project, if you give us a call and chat to Dave Green(who designed the LB30)he will more than likely give you some advice(he normally does even when not asked...) on how to tie everything up... I’m fairly sure he won’t mind you being ‘inspired’ by his output stage... but sometimes he can be a tad grumpy so you takes your chances 😉 

A fine job he did too. Awesome wee amp!

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19 hours ago, Ashdown Engineering said:

Sounds a fun project, if you give us a call and chat to Dave Green(who designed the LB30)he will more than likely give you some advice(he normally does even when not asked...) on how to tie everything up... I’m fairly sure he won’t mind you being ‘inspired’ by his output stage... but sometimes he can be a tad grumpy so you takes your chances 😉 

More great service from a British company we are learning to value and trust.

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16 hours ago, JapanAxe said:

Sorry to disappoint, but an incoming Ampeg PF-50T has somewhat disincentivised the bass amp project. When I do get round to a build, it is now more likely to be based on a Supro guitar amp like this.

Enjoy the pf50t I have the pf20t it's fantastic, so I imagine the 50 is even more awesome. 

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  • 3 years later...
3 hours ago, Nightmares99 said:

Hi, do you have this on file to share via email to me. My little bastard 30 amp is having a few issues with the output stage. Really keen of you can help

 

The link above still works - but, you should drop a line to @Ashdown Engineering anyway via their website, they'll be able to help for sure. 

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