5F2 first tube amp build

[critter01]

Thought i would share my first amp building experience with everyone here.Late last year i acquired an old 1940's "Webster Teletalk".which is a vintage,valve driven office intercom system.here is a short description of what i have done so far.

i stripped the switchboard and all the wire (original cloth coated, stranded) which was still clean and unstained as it had been wrapped up all these years in an outer layer of cloth,will save this for future "vintage upgrades" on a strat and a tele project i have waiting in the wings.

pulled the chassis and took it over to Alan(Unparalled) at Anvil amps to find out which bits were worth keeping.while i was there he gave me the bits i needed to get started.

- Aluminium extrusion - for the chassis

- a clear polycarbonate tag/component board for a 5E3 clone, which was easily modified for the 5F2 circuit that i had planned to build.

started parting out the chassis.at some stage the original PT ,which had been 115 volt ac primary , had been replaced with a 230volt ac primary, which was useful as was the OT, just needed to figure out correct primary/ secondary wiring connections.

the valve compliment consisted of 1 x metal cased 5W4 rectifier,1 x 6F6 output and 1 x metal cased 6J7 pre-amp,all octal.the rectifier and the output valve was used.i already had noval sockets and a few pre-amp valves 12au7/ECC82,12ax7/ECC83 which i can swap around later.

purchased 2 x 1meg pots for the tone and volume controls, i already had pilot light, on/off switch,input/speaker jacks,fuse holder and some IEC connectors that had been salvaged from dead computer power supplies. plenty of hook-up wire from them that i used also.

needed to trim some length of the tag/component board to fit,cut out the hole for the IEC connector,drilled hole for fuse holder,positioned PT and OT,valve sockets on the main part of the chassis for drilling, done at Anvil Amps as i didn't have the right chassis stamps or hole saws,drilled all the holes for the input jack,switch,pilot light and tone/volume controls in front panel of the sub-chassis.

partly assembled the chassis,mounted the unpopulated tag board,front panel(light,switch,pots and input jacks),IEC connector,fuse holder, and headed over to Anvil amps to work out where the best place would be to drill the valve socket holes.

had originally wanted to use 1 of the chokes that i had salvaged,but it was a pain to try and mount it out of view.so following a layout for a 5F2a clone i found on the net( pdf by "Steve Milberger" a regular contributor to the "Blue Guitar website).Alan and i began to populate the tag/component board.

back at home i mounted the valve sockets then worked out the best way to run the filament low-voltage supply and the grounding for tidy lead dress. got lots of info for grounding techniques from articles posted here (Merlin Blencowe) and from the EL84 website

hooked up all the low voltage,made all the connections between output valve,OT,output jack and tagboard and then pre-amp,tone/volume pots and tagboard

i prepared a smaller tagboard for PT 230v supply / 6.3v heater supply and filament virtual ground and mounted that directly underneath the place where i mounted the PT, then every thing was soldered up.

[critter01]

while parting out,all sockets mounted,clear polycarbonate tag board populated,most of the wire hooked up,front panel controls mounted,PT mounted,small label still inside cabinet.

[critter01]

followed an article on the net by Paul Ruby on steps to follow when you have the initial power-up of your creation.after making sure that all PT,230volt IEC,on/off switch and pilot light soldered connections were sound i removed all the valves and powered it up,

put a meter on the IEC connections and the on/off switch to make sure we had 230volts,flicked the switch on for second to observe the pilot glowing brightly then switched it off,no strange burning smells or sparks. success!,this stage of the power-up is good.

flicked the switch on again and put meter on the low voltage filaments all of which read correct with valves removed.(rectifier filament = 5.7v ac,output and preamp filament = 7vac)

then put the meter across the HT from the secondary side of the PT those readings were correct as well.(310v ac across each wire and the PT centre tap)

so i was well pleased with my effort so far.

after asking Alan how to figure out the wiring i decided to just extend the OT hook up wires away from the chassis and drop in see Alan before the first full power-up with all the valves in place then all connections,voltages at various nodes could be checked.

First Alan correctly hooked up the OT, switched it on, a quick prod around and pointed out the dangerous way that i had positioned the on/off switch (both terminals facing up so a careless hand or finger would short out the circuit....zzapp!!)

then we hooked up a speaker,installed the valves and fully powered it up for the first time,all the valves warmed up and there was that familiar glow as the filaments heated up,turned the controls up but... no sound?

eventually we found that i had connected the input jack incorrectly, and apart from some oscillation caused by a tone cap with the incorrect value, which was quickly remedied, i had functioning valve amp!! that had no audible hum at all - sweeeeeet.

back at home i hooked it up to a 10 inch speaker from cheapie SS Chinese amp and proceeded to explore the landscape that is the "Valve sound"

with a 12AU7 in the pre-amp the sound is tight and clean and chimmey when i play my bastardised "Strat" through it.when the volume is turned up to the max, a hint of early 50's no nonsense rock n roll and blues tones are heard.

replace with a 12AX7 and the amps gets more aggressive the more you increase the volume, from early ZZ Topp to early ACDC when maxed out - lovin it!!

at this stage this amp responds great with single coil p/ups,still need to try some Humbuckers and a P90 that i have here.

in the photos the OT can be seen mounted on the chassis,when i did this and powered up again,an annoying 50 hertz hum had developed went back to see Alan again but we cant seem to eliminate it at this stage.he suspects that its coming from the pre-amp section,a suggestion is to change the filament voltage to DC.

cheers