[Harp-L] 1/3W harp amp, was "H Dustcap"

[MARK BURNESS <markwjburness@xxxxxxxxxxxxxx>]

Hi Fjm,

Well, I have a few very low wattage amps now...almost finished prototyping a 
budget 1x8" 0.4W combo, with line out. When totally satisfied (auditioning 
speakers at the minute) I'll post clips, pics, schematic, layout and a BOM at my 
myspace, or forward to anyone whose interested.

But the amp I refererred to in the previous post was originally a 5W, 1xEL84 
made by a UK company Ampmaker (SE5). The power tube voltages were fairly low 
around 250vdc so I rewired the power tube socket to take a 12A#7 tube (both 
triodes wired in parallel) and changed the output transformer to match 
impedances between 12AU7/12BH7/12AY7/12AT7 (wired as a power tube) and an 8ohm 
speaker/cab (~20K:8ohms). Other than that, I just changed one other resistor 
(input stage cathode from 1.5K to 2.2K) & added a line out. It sounds pretty 
good but the full tone stack is a bit superfluous...a simpler, half power 
but more tonally flexible version may be in the pipeline. (Note this 
configuration is not something offered by Ampmaker).

Even with the 4x8" cab it will play clean-ish, full tone at around regular TV 
listening volumes...great for when the ad breaks come on! ;-)

Cheers, Mark.

________________________________
From: fjm <bad_hat@xxxxxxxx>
To: harp-l@xxxxxxxxxx
Sent: Friday, 18 November, 2011 15:46:50
Subject: Re: [Harp-L] H Dustcap

Mark, tell us more about this 1/3 watt amplifier you play though.  fjm