vht/fryette phase inverter???

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Gorhrut
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vht/fryette phase inverter???

Post by 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
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Re: vht/fryette phase inverter???

Post by frankdrebin »

Its probably 12ax7 first stage and cathodyne,12au7 as buffer/amplifier to the power tubes control grids.
Typical HiFi.
pdf64
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Re: vht/fryette phase inverter???

Post by 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?
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xtian
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Re: vht/fryette phase inverter???

Post by xtian »

I build and repair tube amps. http://amps.monkeymatic.com
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ToneMerc
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Re: vht/fryette phase inverter???

Post by ToneMerc »

I wished I still owned his purple 2150 big brother.

TM
Gorhrut
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Re: vht/fryette phase inverter???

Post by Gorhrut »

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
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Re: vht/fryette phase inverter???

Post by 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......
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billyz
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Re: vht/fryette phase inverter???

Post by 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
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Re: vht/fryette phase inverter???

Post by 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
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Re: vht/fryette phase inverter???

Post by Gorhrut »

does this look right if i want to diode rectify the champ circuit?
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billyz
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Re: vht/fryette phase inverter???

Post by 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.
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martin manning
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Re: vht/fryette phase inverter???

Post by martin manning »

Spend some time here: http://www.valvewizard.co.uk
Gorhrut
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Re: vht/fryette phase inverter???

Post by 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.
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rp
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Re: vht/fryette phase inverter???

Post by 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.
Gorhrut wrote: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
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Re: vht/fryette phase inverter???

Post by 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.
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