vht/fryette phase inverter???

[Gorhrut]

i am trying to "clone" the fryette 2/90/2 and make a few changes to pair it with a pre section to make a custom amp head.

with no schematic available, i am stuck trying to reverse engineer this thing from the pcb.......and with only a beginners understanding of guitar amps.

at the same time ive been researching different types of phase inverters, how they work, what they do...etc.

i was wondering does anyone here know what kind of phase inverter setup this amp is using?

the amp uses:
2x 12ax7 for phase inverter
2x 12au7 for driver
4x kt88 for output

again, with my limited knowledge, i believe i can rule out split load/cathodyne because that would only use 1/2 of the 12ax7(correct?) and if that was the case they would only use 1 12ax7 tube in the amp instead of 2.

so im left with paraphase or long tailed pair, opinions?

any other info on the circuit would be greatly appreciated......

[frankdrebin]

Its probably 12ax7 first stage and cathodyne,12au7 as buffer/amplifier to the power tubes control grids.
Typical HiFi.

[pdf64]

This is a stereo 100 watts per channel multi-mode power amp and you're looking to add a pre-amp etc to it?
That seems a seriously complex project!
Page 20 of http://www.mif.pg.gda.pl/homepages/fran ... 88_GEC.pdf shows a 100watt KT88 amp
How about putting it on the back burner and building a Champ type amp first, to develop your skills and understanding?

[xtian]

[img:350:350]http://images.sodahead.com/polls/003645 ... large.jpeg[/img]

[img:500:389]http://www.impactlab.com/wp-content/upl ... ew-764.jpg[/img]

[ToneMerc]

I wished I still owned his purple 2150 big brother.

TM

[Gorhrut]

[img:350:350]http://images.sodahead.com/polls/003645 ... large.jpeg[/img]

[img:500:389]http://www.impactlab.com/wp-content/upl ... ew-764.jpg[/img]

thats the plan!!!

@pdf64, im planning on only building one channel of the amp. i feel like if i had a schematic that i could handle it. maybe i will start off with a simpler build tho.....

@frankdrebin, ill check some hifi schematics and see if that helps me figure it out.



ive got all the components mapped and the traces on the bottom of the board but i cant follow the traces on the top of the board because they're hidden under a couple big filter caps. maybe ill remove them and finish mapping

[Gorhrut]

this is what fryette says about it.....

V1 Input Stage (post volume control).
12AX7 China Phase Inverter.
12AX7WA Russia

V2 Voltage Amp/Driver Stage
12AU7 China Voltage Amp/Driver Stage

V3 Input Stage (post volume control).
12AX7 China Phase Inverter.
12AX7WA Russia

V4 Voltage Amp/Driver Stage
12AU7 China Voltage Amp/Driver Stage

V5-V8 Power Tubes
KT88 Sovtek
KT88 EH
KT88 Svetlana (SED)



so, v1a is the input stage, v1b is the phase inverter, v2a is voltage amp, and v2b is driver......

[billyz]

Is this the amp you had me modify ? If so , I recall you were only using one side.
If that is the case I would build the one on pg 16 of the link pdf64 referred you too.
with that preamp and power amp , you are not getting much distortion from the power amp. So just build a clean power full kt 88 power amp, like pg 16 shows. 50w. If you want a 100+w amp then build a marshall major , hiwatt 200, sound city lb200 etc. or an old style acrosound, there are lots of possibilities.

[Gorhrut]

@billyz, i got a new one. i had to sell that one to cover some bills.

i will start looking at some easier builds for someone at my level.
i still do want to figure out the schematic for this tho.... so i have it when i am ready to make this

[Gorhrut]

does this look right if i want to diode rectify the champ circuit?

[billyz]

No ! , that is a bridge rectifier. Just make it like a standard Fender SS Diode circuit.
Look up the AB763 schematic, say for a bandmaster . Its easy to do and you could do it with a tube rectifier socket even and have it switchable from tube to SS . I have done it with just one 1n4007 per side, but two in series per side might be better( safer ). Fender used 3 per side.

[martin manning]

Spend some time here: http://www.valvewizard.co.uk

[Gorhrut]

checking out champ kits to see which one i want.

in the mean time, ive figured out a lot on the vht circuit. i might have it mostly converted to schematic by tomorrow.....well see.

[rp]

[img:500:389]http://www.impactlab.com/wp-content/upl ... ew-764.jpg[/img][/quote]


That's a mean little lizard. Glad the dinosaurs are extinct.

checking out champ kits to see which one i want.

Suggest you think about a cab made for 10, even a 12, unless the tiny portable thing has more appeal. 5F1 is where it's at IMO. Put the bypass cap on v1.

[pdf64]

checking out champ kits to see which one i want

If you're using a PT intended for a Champ, then best to keep with a 5Y3 rectifier.
If Si diodes were subbed in, the VB+ would increase significantly, thereby opening a can of worms.