CRATE GT80 Amp - UK Vintage Radio Repair and Restoration Discussion Forum

David Simpson · 15th Sep 2017, 3:20 pm

Folks, my son has just acquired one of these for £20. Supposedly u/s, hence the plea - Dad, Dad - can you get it going ? Me - I'm out of my comfort zone - too modern, even though I'm guessing 1980's.
Has anyone got one, or has any info or experience, just to keep me straight. Its a hybrid Valve/ semi-conductor amp with a massive single 12" speaker. I reckon the speaker alone is worth more than £20.

Regards, David

dragonser · 15th Sep 2017, 3:28 pm

Hi,
certainly worth more than £ 20-00 I would think.
I know another Crate ( of a different model ) that I worked on had a faulty transformer, I can't remember if it was output or mains ? But the fault could be something much easier to fix.

Cobaltblue · 15th Sep 2017, 3:48 pm

Circuit which I think is for the same model here https://elektrotanya.com/crate_gt-80.../download.html

The Output is all Solid state it has a few token double triodes of the 12AX7 12AU7 Varieties.
Cheers

Mike T

mark_in_manc · 15th Sep 2017, 4:02 pm

I have a Marshall version of this kind of thing ('valvestate') - it's very versatile, produces a lot of different sounds (clean / dirty and all stops in between, which is the main point of the valve pre-amp) and is a lot more flexible and reliable than other more highly regarded 60s/70s all-valve amps I have used. Fixed, this should be very useful for performance as well as practice.

Do you have some valves to try in it? If the driver turns out to be knackered I can sell you a good 12" unit for 20 quid!

cheers
Mark

David Simpson · 15th Sep 2017, 5:57 pm

Thanks Guys for the info.
I've just got the Users Manual showing the spec & the block diagram. Its full of yanky teeny boppy ampy wampy language, which I don't understand :- "Funky Clean", "Bluesy Dirt", "Warm Tube Crunch", etc. I'll just stick with good old electronics fault-finding.

Regards, David

buggies · 15th Sep 2017, 6:18 pm

Quote:

Originally Posted by Cobaltblue

Circuit which I think is for the same model here https://elektrotanya.com/crate_gt-80.../download.html

Novel idea using the valve filaments for the +16 volt rail fuse...

Herald1360 · 16th Sep 2017, 9:53 am

Quote:

Originally Posted by David Simpson

Thanks Guys for the info.
I've just got the Users Manual showing the spec & the block diagram. Its full of yanky teeny boppy ampy wampy language, which I don't understand :- "Funky Clean", "Bluesy Dirt", "Warm Tube Crunch", etc. I'll just stick with good old electronics fault-finding.

Regards, David

Easy peasy...

How it sounds when new.
How it sounds after a few years on the road.
How it sounds after being tripped over by a drunken roadie.

David Simpson · 16th Sep 2017, 10:35 am

Many thanks George for the circuit diagram link. I've heaps of spare ECC type double triodes, but I'm wondering if the BFP14/BFP9104 Mosfet PA's are easily acquirable these days, if needed ?

Regards, David

David Simpson · 20th Sep 2017, 5:58 pm

More fault finding done - Mains T/F u/s , as are the two rectifying diodes (1N4087's) for the +175V HT line for the valves.
I found that someone had not changed the T/F tappings from 110V to 220V. The Pri now draws 1.5A when my Variac is just set to 40V !
I wonder how easy, if at all, one could get a replacement transformer ?

Regards, David

Ed_Dinning · 20th Sep 2017, 8:55 pm

Hi David, probably a simple reverse engineer and rewind job (without a 110v tap).

Ed

David Simpson · 21st Sep 2017, 11:09 am

Right enough Ed, I guess a rewind for just 240V should do. With the T/F completely disconnected - I used my variac to feed the 85V & 40V bridge rectifier circuits & they seemed fine.
There is loads of space on the chassis & in the cabinet to mount individual mains transformers for each of the three voltage rails (+175V, +&- 85, & +&- 40V). I'll see what I've available or can scrounge meantime.

Regards, David

15th Sep 2017, 3:20 pm	#1
David Simpson Nonode Join Date: Mar 2008 Location: Aberdeen, UK. Posts: 2,853	CRATE GT80 Amp Folks, my son has just acquired one of these for £20. Supposedly u/s, hence the plea - Dad, Dad - can you get it going ? Me - I'm out of my comfort zone - too modern, even though I'm guessing 1980's. Has anyone got one, or has any info or experience, just to keep me straight. Its a hybrid Valve/ semi-conductor amp with a massive single 12" speaker. I reckon the speaker alone is worth more than £20. Regards, David Attached Thumbnails

15th Sep 2017, 3:28 pm	#2
dragonser Heptode Join Date: Aug 2009 Location: Carshalton, Surrey, UK. Posts: 734	Re: CRATE GT80 Amp Hi, certainly worth more than £ 20-00 I would think. I know another Crate ( of a different model ) that I worked on had a faulty transformer, I can't remember if it was output or mains ? But the fault could be something much easier to fix. __________________ Regards Peter B

15th Sep 2017, 3:48 pm	#3
Cobaltblue Moderator Join Date: Dec 2010 Location: Exeter, Devon and Poole, Dorset UK. Posts: 6,865	Re: CRATE GT80 Amp Circuit which I think is for the same model here https://elektrotanya.com/crate_gt-80.../download.html The Output is all Solid state it has a few token double triodes of the 12AX7 12AU7 Varieties. Cheers Mike T __________________ Invisible airwaves crackle with life or at least they used to Mike T BVWS member. www.cossor.co.uk

15th Sep 2017, 4:02 pm	#4
mark_in_manc Octode Join Date: Nov 2011 Location: Manchester, UK. Posts: 1,874	Re: CRATE GT80 Amp I have a Marshall version of this kind of thing ('valvestate') - it's very versatile, produces a lot of different sounds (clean / dirty and all stops in between, which is the main point of the valve pre-amp) and is a lot more flexible and reliable than other more highly regarded 60s/70s all-valve amps I have used. Fixed, this should be very useful for performance as well as practice. Do you have some valves to try in it? If the driver turns out to be knackered I can sell you a good 12" unit for 20 quid! cheers Mark

16th Sep 2017, 10:35 am	#8
David Simpson Nonode Join Date: Mar 2008 Location: Aberdeen, UK. Posts: 2,853	Re: CRATE GT80 Amp Many thanks George for the circuit diagram link. I've heaps of spare ECC type double triodes, but I'm wondering if the BFP14/BFP9104 Mosfet PA's are easily acquirable these days, if needed ? Regards, David

20th Sep 2017, 5:58 pm	#9
David Simpson Nonode Join Date: Mar 2008 Location: Aberdeen, UK. Posts: 2,853	Re: CRATE GT80 Amp More fault finding done - Mains T/F u/s , as are the two rectifying diodes (1N4087's) for the +175V HT line for the valves. I found that someone had not changed the T/F tappings from 110V to 220V. The Pri now draws 1.5A when my Variac is just set to 40V ! I wonder how easy, if at all, one could get a replacement transformer ? Regards, David

20th Sep 2017, 8:55 pm	#10
Ed_Dinning Dekatron Join Date: Jan 2004 Location: Newcastle upon Tyne, Tyne & Wear, UK. Posts: 8,194	Re: CRATE GT80 Amp Hi David, probably a simple reverse engineer and rewind job (without a 110v tap). Ed

21st Sep 2017, 11:09 am	#11
David Simpson Nonode Join Date: Mar 2008 Location: Aberdeen, UK. Posts: 2,853	Re: CRATE GT80 Amp Right enough Ed, I guess a rewind for just 240V should do. With the T/F completely disconnected - I used my variac to feed the 85V & 40V bridge rectifier circuits & they seemed fine. There is loads of space on the chassis & in the cabinet to mount individual mains transformers for each of the three voltage rails (+175V, +&- 85, & +&- 40V). I'll see what I've available or can scrounge meantime. Regards, David