Junk box low watt amp build

[dougietamson]

Originally Posted by G6Tanuki

It's always good to experiment - take the theoretical equations/calculations as a reference-point but don't ever think it's a sin to deviate from them!

Valve power-amplifier matching is always a bit of a fudge: what gives the highest fidelity and what gives the best power-transfer-into-the-load are not always the same.

Most guitarists consider the whole guitar->pickup->amp->speaker path as part of their 'instrument' so seeking perfectly-linear, distortion-free amplification takes a back-row if they can coerce/overdrive an amp/speaker combo in order to get the particular sound they want.

I'm sure Eric Clapton, "Snowy" White, Mike Oldfield or Carlos Santana didn't get hung-up about issues of impedance-matching in their amplifiers.

I've been learning guitar for 42 years, amp building for only 2 years.

Here's another sound test I did today, going for the creamy overdrive of little pentodes pushed and pulled to distraction but very low volume.

Albatros interpretation , Strat in-between pickup 2/3 out of phase -> small pentode pp amp -> 2x12" speakers wired in series for 16 Ohms -> Sure SM57 -> firewire audio interface -> logic pro + lot of reverb -> mp3

[Herald1360]

Originally Posted by dougietamson

Hmm

I have 5xEF91 but only 3 B7G sockets.

Doug

Doug,



I'm following this thread with some interest.....



If you'd like half a dozen Cinch paxolin B7G sockets and a couple of nicer mil surplus skirted ones in a Jiffy bag just PM me your address.


If you fancy blowing your socks off (ish) with a heady 10W I could chuck in a couple of unbranded NOS USA 6005 (6AQ5 equiv) toobs for luck.

[dougietamson]

Originally Posted by Herald1360

Doug,



I'm following this thread with some interest.....



If you'd like half a dozen Cinch paxolin B7G sockets and a couple of nicer mil surplus skirted ones in a Jiffy bag just PM me your address.


If you fancy blowing your socks off (ish) with a heady 10W I could chuck in a couple of unbranded NOS USA 6005 (6AQ5 equiv) toobs for luck.

Thanks Chris, very kind of you, those 6AQ5/EL90 equivalents would make a great Fender deluxe reverb style project (though best not run them at Fender plate voltage of >350v) for my middle son.

PM sent

Doug

[dougietamson]

Some good progress being made...
I posted a thread on a US based guitar forum to get feedback about the tone of the EF80/EF184 low watt amp.

RobRob, one of the forum member has just provided load lines for an EF80 and a full turret board layout when using the EF80 in the push pull output stage, including a readily available output transformer. The preamp and PI stages are from the Fender Bassman amp.

Some say the Fender Bassman was the amp that 3 young radio hams in and around London were "inspired" by to create the famous Marshall JTM45 in 1963, others have used the word "copy". Marshall of course was just the shop owner.

https://robrobinette.com/Drawing_Tub...Lines.htm#EF80

I'll try a 240 Ohm cathode resisters in-place of the 100 Ohm one I've been using. Maybe add a switch to toggle between the two.

Doug

[dougietamson]

The borrowed OT is back in it's amp, replaced with a mains toroidal...
I used a £10 dual 115v pri/dual 12v sec 15VA
The 2 primaries are tied together 115-0-115 to give a CT.
The 2 12v secondaries were easy to get at, these are wound bifilar. I unwound 120 turns and added a taps to give a ratio of 38:1 then unwound a further 60 turns to give 57:1.

Amp still sounding good, no distortion seen on a 60Hz sine wave until it's over driven.

Doug