Grampian 552B amplifier - UK Vintage Radio Repair and Restoration Discussion Forum

rontech · 3rd Oct 2017, 9:56 am

I have recently acquired from a friend a PA mixer/amplifier. Grampian Model 552B

There is some information, largely pics, on the internet but I have not found a circuit diagram.

The valve line up is 2 x EF86 / 1 x ECC83 / 1 x ECC81 / 2 x KT66 / 1 x GZ32

It appears to a conventional ( mid 1950's ? ) 15 - 20 watt push pull output
design. At least one of the EF86 appears to be a boost stage for two mic
inputs which have a couple of matching transformers low impedance to high
high probably for ribbon or low impedance mc mikes.

The op transformer is a simple ct primary type with no taps for distributed load or ultra linear operation.

4, 8, 15 and 100v line secondary.

I would appreciate a link to a circuit diagram if anyone can help.

Not sure if I will attempt restoration or dismantle as a parts resource.

kevinaston1 · 3rd Oct 2017, 10:28 am

There was a Grampian 562 discussed about six years ago by a member, I think it was a similar unit, only a single input; but he did post a circuit diagram for it.

Kevin

Edward Huggins · 3rd Oct 2017, 3:58 pm

Restoration might be fine if you wanted to use this as a Mono amp in its own right.
It could be used as a Monoblock for a stereo pair, but building the second channel would be very expensive. Also some tweaking of the coupling components might be needed to make this more HiFi than PA.

rontech · 3rd Oct 2017, 6:38 pm

Thank's for that Kevin.

I found that reference too. From the pic supplied I think the valve line up was different as well.

rontech · 5th Oct 2017, 9:48 am

Thanks Edward.

The chassis and cover is a pretty large industrial type item which I would not want for hi fi purposes. My thoughts are to use the hefty HT transformer, get new electrolytics and use some of the B9G valves plus a KT66 and construct a regulated HT power pack. I am thinking a new chassis / case and adding a smoothing choke in the new version.

Edward Huggins · 5th Oct 2017, 10:43 am

An ideal solution for this Battleship of a Beast.

I think some may call this, er, "repurposing".....?!

Hartley118 · 5th Oct 2017, 11:30 am

On the other hand, once you've got it functioning again, this could be just the amp for those occasions when you're asked as the local 'tech guy' 'just' to fix up a PA for the Village Fair on the playing fields.

Or as sometimes happens to me, a neighbour asks in a hurry if you can amplify their daughter's iPhone music for a party that very evening!

I hang on to my RSC A10 30 watt valve amp in order to respond on those occasions.

You'd also of course need one or two unburstable speakers to go with the amp!

Martin

rontech · 5th Oct 2017, 6:36 pm

I am old enough to have had my fill of "Can you justs?"

crackle · 5th Oct 2017, 11:35 pm

If it's any help I have added the schematic for the Grampian 562/7/D to my web page.
http://www.kbmuseum.org.uk/other_ser...562-7-gram.pdf

Mike

rontech · 6th Oct 2017, 4:45 pm

Thanks Mike.
I will study and compare with my own amp.

3rd Oct 2017, 9:56 am	#1
rontech Heptode Join Date: Jun 2017 Location: Southport, Merseyside, UK. Posts: 646	Grampian 552B amplifier I have recently acquired from a friend a PA mixer/amplifier. Grampian Model 552B There is some information, largely pics, on the internet but I have not found a circuit diagram. The valve line up is 2 x EF86 / 1 x ECC83 / 1 x ECC81 / 2 x KT66 / 1 x GZ32 It appears to a conventional ( mid 1950's ? ) 15 - 20 watt push pull output design. At least one of the EF86 appears to be a boost stage for two mic inputs which have a couple of matching transformers low impedance to high high probably for ribbon or low impedance mc mikes. The op transformer is a simple ct primary type with no taps for distributed load or ultra linear operation. 4, 8, 15 and 100v line secondary. I would appreciate a link to a circuit diagram if anyone can help. Not sure if I will attempt restoration or dismantle as a parts resource.

3rd Oct 2017, 10:28 am	#2
kevinaston1 Hexode Join Date: Aug 2014 Location: Featherstone, West Yorkshire, UK. Posts: 386	Re: Grampian 552b amplifier There was a Grampian 562 discussed about six years ago by a member, I think it was a similar unit, only a single input; but he did post a circuit diagram for it. Kevin

3rd Oct 2017, 3:58 pm	#3
Edward Huggins Dekatron Join Date: Sep 2015 Location: Southwold, Suffolk, UK. Posts: 8,327	Re: Grampian 552b amplifier Restoration might be fine if you wanted to use this as a Mono amp in its own right. It could be used as a Monoblock for a stereo pair, but building the second channel would be very expensive. Also some tweaking of the coupling components might be needed to make this more HiFi than PA. __________________ Edward.

3rd Oct 2017, 6:38 pm	#4
rontech Heptode Join Date: Jun 2017 Location: Southport, Merseyside, UK. Posts: 646	Re: Grampian 552B amplifier Thank's for that Kevin. I found that reference too. From the pic supplied I think the valve line up was different as well.

5th Oct 2017, 9:48 am	#5
rontech Heptode Join Date: Jun 2017 Location: Southport, Merseyside, UK. Posts: 646	Re: Grampian 552B amplifier Thanks Edward. The chassis and cover is a pretty large industrial type item which I would not want for hi fi purposes. My thoughts are to use the hefty HT transformer, get new electrolytics and use some of the B9G valves plus a KT66 and construct a regulated HT power pack. I am thinking a new chassis / case and adding a smoothing choke in the new version.

5th Oct 2017, 10:43 am	#6
Edward Huggins Dekatron Join Date: Sep 2015 Location: Southwold, Suffolk, UK. Posts: 8,327	Re: Grampian 552B amplifier An ideal solution for this Battleship of a Beast. I think some may call this, er, "repurposing".....?! __________________ Edward.

5th Oct 2017, 11:30 am	#7
Hartley118 Nonode Join Date: Aug 2015 Location: Cambridge, Cambs. UK. Posts: 2,198	Re: Grampian 552B amplifier On the other hand, once you've got it functioning again, this could be just the amp for those occasions when you're asked as the local 'tech guy' 'just' to fix up a PA for the Village Fair on the playing fields. Or as sometimes happens to me, a neighbour asks in a hurry if you can amplify their daughter's iPhone music for a party that very evening! I hang on to my RSC A10 30 watt valve amp in order to respond on those occasions. You'd also of course need one or two unburstable speakers to go with the amp! Martin __________________ BVWS Member

5th Oct 2017, 6:36 pm	#8
rontech Heptode Join Date: Jun 2017 Location: Southport, Merseyside, UK. Posts: 646	Re: Grampian 552B amplifier I am old enough to have had my fill of "Can you justs?"

5th Oct 2017, 11:35 pm	#9
crackle Rest in Peace Join Date: Mar 2011 Location: Basildon, Essex, UK. Posts: 4,100	Re: Grampian 552B amplifier If it's any help I have added the schematic for the Grampian 562/7/D to my web page. http://www.kbmuseum.org.uk/other_ser...562-7-gram.pdf Mike

6th Oct 2017, 4:45 pm	#10
rontech Heptode Join Date: Jun 2017 Location: Southport, Merseyside, UK. Posts: 646	Re: Grampian 552B amplifier Thanks Mike. I will study and compare with my own amp.