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Vintage Audio (record players, hi-fi etc) Amplifiers, speakers, gramophones and other audio equipment. |
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14th Mar 2018, 6:36 pm | #1 |
Tetrode
Join Date: Sep 2017
Location: Bridgend, Mid Glamorgan, UK.
Posts: 66
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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 |
14th Mar 2018, 7:14 pm | #2 |
Guest
Posts: n/a
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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.
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15th Mar 2018, 1:50 am | #3 |
Nonode
Join Date: Jun 2014
Location: Bristol, UK.
Posts: 2,074
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Re: Speaker advice.
As above - 6V6s are amongst my favourite output valves - let us know how it sounds.
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15th Mar 2018, 9:47 am | #4 |
Tetrode
Join Date: Sep 2017
Location: Bridgend, Mid Glamorgan, UK.
Posts: 66
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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 |
Dekatron
Join Date: Jul 2009
Location: Sleaford, Lincs. UK.
Posts: 7,667
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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.
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16th Mar 2018, 10:17 am | #6 |
Heptode
Join Date: Jun 2017
Location: Southport, Merseyside, UK.
Posts: 646
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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 |
Tetrode
Join Date: Sep 2017
Location: Bridgend, Mid Glamorgan, UK.
Posts: 66
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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.
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17th Mar 2018, 8:26 am | #8 |
Banned
Join Date: Jun 2015
Location: Mareeba, North Queensland, Australia
Posts: 2,704
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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 |
Heptode
Join Date: Jun 2017
Location: Southport, Merseyside, UK.
Posts: 646
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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 |
Dekatron
Join Date: Apr 2012
Location: Wiltshire, UK.
Posts: 14,005
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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 |
Tetrode
Join Date: Sep 2017
Location: Bridgend, Mid Glamorgan, UK.
Posts: 66
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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 |
Dekatron
Join Date: Sep 2015
Location: Southwold, Suffolk, UK.
Posts: 8,335
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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.
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Edward. |
15th May 2018, 3:46 pm | #13 |
Tetrode
Join Date: Sep 2017
Location: Bridgend, Mid Glamorgan, UK.
Posts: 66
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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.
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15th May 2018, 5:04 pm | #14 |
Dekatron
Join Date: Sep 2015
Location: Southwold, Suffolk, UK.
Posts: 8,335
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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?
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Edward. |
15th May 2018, 6:06 pm | #15 |
Tetrode
Join Date: Sep 2017
Location: Bridgend, Mid Glamorgan, UK.
Posts: 66
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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.
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17th May 2018, 1:42 pm | #16 |
Heptode
Join Date: Jan 2016
Location: Wolverhampton, West Midlands, UK.
Posts: 777
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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 |
Tetrode
Join Date: Sep 2017
Location: Bridgend, Mid Glamorgan, UK.
Posts: 66
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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 |
20th May 2018, 7:35 pm | #18 |
Guest
Posts: n/a
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Re: Speaker advice.
Good result, it is great to build something and then use it in anger!
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20th May 2018, 7:53 pm | #19 |
Tetrode
Join Date: Sep 2017
Location: Bridgend, Mid Glamorgan, UK.
Posts: 66
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Re: Speaker advice.
It sounds really well and clean at low volumes but breaks up as you drive it a bit.
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20th May 2018, 8:33 pm | #20 |
Dekatron
Join Date: Sep 2015
Location: Southwold, Suffolk, UK.
Posts: 8,335
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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.
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Edward. |