Speaker advice. - UK Vintage Radio Repair and Restoration Discussion Forum

Singlofty · 14th Mar 2018, 6:36 pm

I picked this 12 inch speaker up a while back and I'd like to fit it into a guitar amp build. The amp will be based on YouTube "uncle dougs" unknown amp video which is a 6v6 pp pre war design. The speaker has no output or impedance markings and measures 5.5 ohms. I was hoping to use an output transformer I have which will handle 15 watts into 8 ohms. Any thoughts, observations gratefully received.
Cheers
Dave

14th Mar 2018, 7:14 pm

5.5 ohms DC is about what 8 ohms would measure and I would suspect a 12" 'speaker would handle 15 watts easily. You have the two most expensive bits already, go and build away.

RojDW48 · 15th Mar 2018, 1:50 am

As above - 6V6s are amongst my favourite output valves - let us know how it sounds.

Singlofty · 15th Mar 2018, 9:47 am

Thanks for the replies, my main concern was the power specification. The amp is an interesting design that has two inputs, a 6j7 pentode and a 6c5 triode. Will keep you posted.
Dave

Diabolical Artificer · 16th Mar 2018, 9:58 am

That speaker should handle 15w with ease. I have one in a FAL cab in the shed.

Know the amp you mention, he builds nice amps.

Andy.

rontech · 16th Mar 2018, 10:17 am

I have sourced some components; 6V6's; p-p output transformer; ht transformer ( the latter for 110V - 120V mains though ); from old Bell and Howel, early ( valve amp ) 16 mm sound projectors.

They have three 6V6 valves, 2 for -pp output, the third is for a high frequency oscillator to power the exciter lamp for the optical sound tracks. Also 6J7 or mullard EF37A; 6SL7GT.

Look for model 601's and later they are usually cheap to buy.

Hope this is of interest / help.

Singlofty · 16th Mar 2018, 8:24 pm

Where did you find the B and H units, I bought Russian equivalents, the output valves, phase splitter and one of the input valves delivered for less than a 6V6 would have cost on eBay.

joebog1 · 17th Mar 2018, 8:26 am

Myself? I think a very fine score!!

B&H had fairly chunky stuff and should work a treat !!!

Joe

rontech · 18th Mar 2018, 8:20 pm

I have been a member of a local cine / video society since the early 1960's. We meet in a church hall and the church authorities demanded we cleared out the loft

There were 3 B&H sound projectors to scrap 2 x Model 601 and 1 x Model 63 something?

1 x B&H 12" loudspeaker with hefty magnet. I have dismantled all 3 the resulting in lots of BA nuts and bolts, valveholders, transformers useful brackets and a couple of stout steel chassis with octal valve cut outs.

G6Tanuki · 18th Mar 2018, 8:40 pm

One thing to check: given that your speaker appears to be 8-Ohm impedance, does the ex-projector output transformer you intend to use with your pair of 6V6 have an 8-Ohm secondary winding?

A lot of valve gear up to the 1970s was designed to drive speakers with 3- or 4-Ohm impedance.

Singlofty · 18th Mar 2018, 10:00 pm

Sorry we seem to be talking about crossed posts. The output transformer I'm using came out of a fender blues special amp that had been upgraded. It's rated at 15 watts which should be plenty for this build.
Cheers
Dave

Edward Huggins · 18th Mar 2018, 10:53 pm

For 2 x 6V6s in PP, a 15 watt OP transformer will be just fine. But not for more powerful bigger valves.

Singlofty · 15th May 2018, 3:46 pm

Some pics of the finished amp. With a 1kh input into an 8 ohm dummy load it starts to clip around 10v output. The pentode input sounds slightly brighter than the triode but not much difference in volume.

Edward Huggins · 15th May 2018, 5:04 pm

That beefy speaker will handle 2 x PP 6V6s well. My only concern is that there are only the 6J7 and 6C5 ahead of them. Will there be sufficient gain or will you be using a high-output Guitar pick up?

Singlofty · 15th May 2018, 6:06 pm

Plenty loud enough for home use, which is the only use I will give it. My first attempt at a scratch build so I'm happy it works at all.

Bufo Bill · 17th May 2018, 1:42 pm

That is a mighty fine build Lofty! Congratulations. Got to love a Windsor Davies reference too.
Bill.

Singlofty · 20th May 2018, 4:04 pm

Thanks for all of the advice. My next plan is a Selmer Commodore recreation but I've got to work out adding a magic eye tremelo to it. Any way here's a pic of the speaker mounted in the cabinet.
Cheers
Dai

20th May 2018, 7:35 pm

Good result, it is great to build something and then use it in anger!

Singlofty · 20th May 2018, 7:53 pm

It sounds really well and clean at low volumes but breaks up as you drive it a bit.

Edward Huggins · 20th May 2018, 8:33 pm

This is highly unlikely to be anything to do with that good speaker, but maybe overdemands on the HT supply on your amp.

14th Mar 2018, 6:36 pm	#1
Singlofty Tetrode Join Date: Sep 2017 Location: Bridgend, Mid Glamorgan, UK. Posts: 66	Speaker advice. I picked this 12 inch speaker up a while back and I'd like to fit it into a guitar amp build. The amp will be based on YouTube "uncle dougs" unknown amp video which is a 6v6 pp pre war design. The speaker has no output or impedance markings and measures 5.5 ohms. I was hoping to use an output transformer I have which will handle 15 watts into 8 ohms. Any thoughts, observations gratefully received. Cheers Dave Attached Thumbnails

14th Mar 2018, 7:14 pm	#2
Guest Guest Posts: n/a	Re: Speaker advice. 5.5 ohms DC is about what 8 ohms would measure and I would suspect a 12" 'speaker would handle 15 watts easily. You have the two most expensive bits already, go and build away.

15th Mar 2018, 1:50 am	#3
RojDW48 Nonode Join Date: Jun 2014 Location: Bristol, UK. Posts: 2,074	Re: Speaker advice. As above - 6V6s are amongst my favourite output valves - let us know how it sounds. __________________ '....don't go mistaking Paradise for that home across the road!' (Bob Dylan)

15th Mar 2018, 9:47 am	#4
Singlofty Tetrode Join Date: Sep 2017 Location: Bridgend, Mid Glamorgan, UK. Posts: 66	Re: Speaker advice. Thanks for the replies, my main concern was the power specification. The amp is an interesting design that has two inputs, a 6j7 pentode and a 6c5 triode. Will keep you posted. Dave

16th Mar 2018, 9:58 am	#5
Diabolical Artificer Dekatron Join Date: Jul 2009 Location: Sleaford, Lincs. UK. Posts: 7,662	Re: Speaker advice. That speaker should handle 15w with ease. I have one in a FAL cab in the shed. Know the amp you mention, he builds nice amps. Andy. __________________ Curiosity hasn't killed this cat...so far.

16th Mar 2018, 10:17 am	#6
rontech Heptode Join Date: Jun 2017 Location: Southport, Merseyside, UK. Posts: 646	Re: Speaker advice. I have sourced some components; 6V6's; p-p output transformer; ht transformer ( the latter for 110V - 120V mains though ); from old Bell and Howel, early ( valve amp ) 16 mm sound projectors. They have three 6V6 valves, 2 for -pp output, the third is for a high frequency oscillator to power the exciter lamp for the optical sound tracks. Also 6J7 or mullard EF37A; 6SL7GT. Look for model 601's and later they are usually cheap to buy. Hope this is of interest / help.

16th Mar 2018, 8:24 pm	#7
Singlofty Tetrode Join Date: Sep 2017 Location: Bridgend, Mid Glamorgan, UK. Posts: 66	Re: Speaker advice. Where did you find the B and H units, I bought Russian equivalents, the output valves, phase splitter and one of the input valves delivered for less than a 6V6 would have cost on eBay.

17th Mar 2018, 8:26 am	#8
joebog1 Banned Join Date: Jun 2015 Location: Mareeba, North Queensland, Australia Posts: 2,704	Re: Speaker advice. Myself? I think a very fine score!! B&H had fairly chunky stuff and should work a treat !!! Joe

18th Mar 2018, 8:20 pm	#9
rontech Heptode Join Date: Jun 2017 Location: Southport, Merseyside, UK. Posts: 646	Re: Speaker advice. I have been a member of a local cine / video society since the early 1960's. We meet in a church hall and the church authorities demanded we cleared out the loft There were 3 B&H sound projectors to scrap 2 x Model 601 and 1 x Model 63 something? 1 x B&H 12" loudspeaker with hefty magnet. I have dismantled all 3 the resulting in lots of BA nuts and bolts, valveholders, transformers useful brackets and a couple of stout steel chassis with octal valve cut outs.

18th Mar 2018, 8:40 pm	#10
G6Tanuki Dekatron Join Date: Apr 2012 Location: Wiltshire, UK. Posts: 13,998	Re: Speaker advice. One thing to check: given that your speaker appears to be 8-Ohm impedance, does the ex-projector output transformer you intend to use with your pair of 6V6 have an 8-Ohm secondary winding? A lot of valve gear up to the 1970s was designed to drive speakers with 3- or 4-Ohm impedance.

18th Mar 2018, 10:00 pm	#11
Singlofty Tetrode Join Date: Sep 2017 Location: Bridgend, Mid Glamorgan, UK. Posts: 66	Re: Speaker advice. Sorry we seem to be talking about crossed posts. The output transformer I'm using came out of a fender blues special amp that had been upgraded. It's rated at 15 watts which should be plenty for this build. Cheers Dave

18th Mar 2018, 10:53 pm	#12
Edward Huggins Dekatron Join Date: Sep 2015 Location: Southwold, Suffolk, UK. Posts: 8,328	Re: Speaker advice. For 2 x 6V6s in PP, a 15 watt OP transformer will be just fine. But not for more powerful bigger valves. __________________ Edward.

15th May 2018, 3:46 pm	#13
Singlofty Tetrode Join Date: Sep 2017 Location: Bridgend, Mid Glamorgan, UK. Posts: 66	Re: Speaker advice. Some pics of the finished amp. With a 1kh input into an 8 ohm dummy load it starts to clip around 10v output. The pentode input sounds slightly brighter than the triode but not much difference in volume. Attached Thumbnails

15th May 2018, 5:04 pm	#14
Edward Huggins Dekatron Join Date: Sep 2015 Location: Southwold, Suffolk, UK. Posts: 8,328	Re: Speaker advice. That beefy speaker will handle 2 x PP 6V6s well. My only concern is that there are only the 6J7 and 6C5 ahead of them. Will there be sufficient gain or will you be using a high-output Guitar pick up? __________________ Edward.

15th May 2018, 6:06 pm	#15
Singlofty Tetrode Join Date: Sep 2017 Location: Bridgend, Mid Glamorgan, UK. Posts: 66	Re: Speaker advice. Plenty loud enough for home use, which is the only use I will give it. My first attempt at a scratch build so I'm happy it works at all.

17th May 2018, 1:42 pm	#16
Bufo Bill Heptode Join Date: Jan 2016 Location: Wolverhampton, West Midlands, UK. Posts: 777	Re: Speaker advice. That is a mighty fine build Lofty! Congratulations. Got to love a Windsor Davies reference too. Bill.

20th May 2018, 4:04 pm	#17
Singlofty Tetrode Join Date: Sep 2017 Location: Bridgend, Mid Glamorgan, UK. Posts: 66	Re: Speaker advice. Thanks for all of the advice. My next plan is a Selmer Commodore recreation but I've got to work out adding a magic eye tremelo to it. Any way here's a pic of the speaker mounted in the cabinet. Cheers Dai Attached Thumbnails

20th May 2018, 7:35 pm	#18
Guest Guest Posts: n/a	Re: Speaker advice. Good result, it is great to build something and then use it in anger!

20th May 2018, 7:53 pm	#19
Singlofty Tetrode Join Date: Sep 2017 Location: Bridgend, Mid Glamorgan, UK. Posts: 66	Re: Speaker advice. It sounds really well and clean at low volumes but breaks up as you drive it a bit.

20th May 2018, 8:33 pm	#20
Edward Huggins Dekatron Join Date: Sep 2015 Location: Southwold, Suffolk, UK. Posts: 8,328	Re: Speaker advice. This is highly unlikely to be anything to do with that good speaker, but maybe overdemands on the HT supply on your amp. __________________ Edward.