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 Playmaster 103 guitar amplifier
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 Return to top of page · Post #: 1 · Written at 12:05:30 PM on 11 September 2018.
Sue's avatar
 Sue
 Location: Daylesford, VIC
 Member since 13 January 2011
 Member #: 809
 Postcount: 311

I've decided to have a crack at the EA Playmaster 102/103 combo guitar amplifier. I have most of the parts I need in my junk hoard, and why should I let that stuff gather dust? Technically, the 103 is a twin channel combo with two completely separate amplifier and speaker systems built in. The amps are 12 watt ultra-linear push-pull using 6GW8's, and can be ganged to give 24 watts total, or one can be used for reverb, vocals, etc. Tremolo and reverb are built-in.


 
 Return to top of page · Post #: 2 · Written at 3:30:23 PM on 11 September 2018.
GTC's avatar
 GTC
 Location: Sydney, NSW
 Member since 28 January 2011
 Member #: 823
 Postcount: 5263

I say go right ahead but, as with any EA project, check subsequent issues for errata and notes, and any comments that builders wrote in with.

When I was in high school I built the Playmaster 117 for a school mate in the garage at home. It pushed out 60W and I recall the woman next door complaining about the "noise" when he came around to test it. It used 6DQ6A's. A mate of mine with carpentry skills built a speaker box out of plywood.

I still remember trudging home via public transport and shanks' pony with a large box of components for it purchased from Radio Despatch at Broadway. Those were the days when guys behind the counter fetched every part from stock, including climbing ladders to get components from the top shelves and hand wrote invoices on yellow paper. The stinger was always the sales tax added to the sub subtotal. I seem to recall handing over around $100 that he stumped up for the parts, which would be $1,000 or more today.


 
 Return to top of page · Post #: 3 · Written at 4:31:44 PM on 11 September 2018.
Ian Robertson's Gravatar
 Location: Belrose, NSW
 Member since 31 December 2015
 Member #: 1844
 Postcount: 1291

Yes I built a couple of those too, for mates at school. A couple of train trips to get parts come to mind.

I recall one of my mates reckoned it was too "clean" for lead work. Thought afterwards that removing the negative feedback would have solved that issue.


 
 Return to top of page · Post #: 4 · Written at 6:44:48 PM on 11 September 2018.
Fred Lever's Gravatar
 Location: Toongabbie, NSW
 Member since 19 November 2015
 Member #: 1828
 Postcount: 574

Good on you Sue, go for it!
The design was a bit of a Hi-Fi hangover with the output transformer and feedback but a handy bit of kit.
Ok for a small hall or private use and the speakers used are the key, they have be efficient guitar speakers like SC used on that A frame thing in the latest issue. They are spot on with their comments in that article.
Back in the day I used Rola 12PX, 12EUG or something like that or more expensive types.
As I noted in my last bass amp I tried one of the ebay do it all speakers, what a joke, it got bent in the mail, do go near that rubbish and forget Hi-Fi speakers they are all 90db or lower sensitivity.
I never did make a 102/3 as I needed 100 watts or more for my guitar/Pa amps so made a couple of 107's with 6DQ6 but in the end had to shift to 6CA7's and lots of volts!
Again , go for it!
Fred.


 
 Return to top of page · Post #: 5 · Written at 11:43:54 AM on 12 September 2018.
Sue's avatar
 Sue
 Location: Daylesford, VIC
 Member since 13 January 2011
 Member #: 809
 Postcount: 311

The "clean" sound appeals to me, it means the amp can be used for instruments other than guitar once I've reduced the built-in 140Hz roll-off slightly, and it doesn't need to be window-rattling loud. The speakers I have on hand are a huge cast alloy 12'' Yamaha/Pioneer JA3002 woofer from an organ, and the choice of a Rola CM8X or an AWA/MSP 8TACX for the 8'' reverb speaker, which will also act as a tweeter when the two amps are ganged. The Rola is the early version rated at 16 watts, but I'm not sure if the MSP will handle that much, the cone looks a bit flimsy.

The first step is to get a chassis made, unless someone's got a discard somewhere. RTV&H published blueprints for this, but I'll have to work from the photos. The idea is make the drillings and cut outs on the original design, but use the odd parts I have for a test version. There's no point in spending big money on guitar transformers and chassis-mount capacitors unless I'm sure it'll work properly.


 
 Return to top of page · Post #: 6 · Written at 2:00:28 PM on 12 September 2018.
Fred Lever's Gravatar
 Location: Toongabbie, NSW
 Member since 19 November 2015
 Member #: 1828
 Postcount: 574

Hi Sue, your speakers sound ok to me so long as you keep the sound clean and don't square wave it.
Doing that will take out the voice coils real fast.
I had to cater to musos who just turned all the knobs up to 11 and went flat out trying to drown out all the screaming kids!
My thinking does get coloured a bit by that!
The output trannies don't need to be anything special just ones that suited the valve with impedance matching close enough and the power level.
A couple of years ago I ordered a 40 watt tranny from one of the specialist suppliers to see what he would come up with.
What I got was wound exactly like a battery charger tranny! One primary CT and then one secondary over the top with taps. Plain steel thick EI stacking. So much for interleaved primary and secondary windings and grain oriented hi mu thin laminations. Price was ok and its still going with a pair of 6CA7's hanging off it.
Yeah just get a sheet of tin like a discarded microwave oven cover and mark that out for all the holes and just bash it into shape. I love those kerb side microwaves they have good sheet steel, some fancy switches and bits, 240 coloured cables and 2kV rated capacitors for your next CRT CRO/TV project!
Fred.


 
 Return to top of page · Post #: 7 · Written at 2:39:35 PM on 12 September 2018.
GTC's avatar
 GTC
 Location: Sydney, NSW
 Member since 28 January 2011
 Member #: 823
 Postcount: 5263

The first step is to get a chassis made

Have a word with Tony, here: http://silversprings.net.au/


 
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