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Old 26th Jul 2018, 8:57 pm   #61
bikerhifinut
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Default Re: Beam Echo Avantic SPA11 restoration. Help please!

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Originally Posted by ChrisMarsden View Post
Any tips for valve socket cleaning? And what about potentiometers?
De oxit is what I use for most electrical contact cleaning. Its expensive but a little goes a long way. If I feel the need to clean a valve socket contacts a SMALL amount of de oxit in conjunction with a scrap valve inserted and removed a few times usually does the business. Then allow it to evaporate completely before switch on.
For pots, if noisy, again I use a bit of deoxit squirted inside and a few cycles of the wiper should sort out a dirty/noisy track. I'd only clean pots if there was an issue with noise or intermittent contact.

Other switch cleaners/lubricants are available. Servisol springs to mind and comes in various recipes. Most are based on IPA (iso propyl Alcohol not expensive beer!) afaik.

Whatever you do NEVER use WD40 on sensitive electronic circuits. It can make a bit of a mess amongst other negative aspects.


A.
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Old 10th Aug 2018, 8:21 am   #62
ChrisMarsden
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Default Re: Beam Echo Avantic SPA11 restoration. Help please!

Lamp limiter constructed!

However I'm finding a 100w tungsten bulb hard to find. Amazon seem to be the only place and then in packs of 10 . Do any high street shops in the UK still sell 100w bulbs? can i get away with a 60w? How about two 60w in series?
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Old 10th Aug 2018, 8:56 am   #63
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Default Re: Beam Echo Avantic SPA11 restoration. Help please!

I don't use a lamp limiter myself. But if you wanted to make something close to a 100W bulb using two 60's then you'd wire them in parallel, not in series (bulbs are designed to run from a fixed voltage supply, so higher wattage needs lower resistance).

Cheers,

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Old 10th Aug 2018, 9:18 am   #64
ChrisMarsden
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Default Re: Beam Echo Avantic SPA11 restoration. Help please!

Parallel it is! Can anyone confirm the speaker din socket pinouts? Looking at the back which is pin 1, 2,3 & 4?
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Old 10th Aug 2018, 6:25 pm   #65
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Default Re: Beam Echo Avantic SPA11 restoration. Help please!

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Do any high street shops in the UK still sell 100w bulbs?
Not sure if they are everywhere but "rough service" or "heavy duty" should still be around e.g.
https://www.poundstretcher.co.uk/100...uty-light-bulb
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Old 11th Aug 2018, 8:23 am   #66
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Default Re: Beam Echo Avantic SPA11 restoration. Help please!

"Lamp limiter constructed! " Well done.

Din plugs/sockets sometimes have tiny numbers on the back, but there's a chart here - https://www.electronics2000.co.uk/pin-out/dincon.php and here - https://en.wikipedia.org/wiki/DIN_connector You should be able to figure out what's what when you take the top/bottom off and follow the wires from the OPT (output transformer)

Good to see you making progress, Andy.
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Old 11th Aug 2018, 8:38 am   #67
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Default Re: Beam Echo Avantic SPA11 restoration. Help please!

Quote:
Din plugs/sockets sometimes have tiny numbers on the back, but there's a chart here -
As these are NOT DIN I don't think that will help in this case, but a useful chart for reference. The circuit diagram shows the socket and is numbered. Tracing which wire goes to each tag should not be difficult. These plugs are like those on Black Boxes and amps/players of similar vintage and used for all sorts of purposes.
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Old 11th Aug 2018, 10:30 am   #68
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Default Re: Beam Echo Avantic SPA11 restoration. Help please!

Did you test the output transformer primary continuity?
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Old 11th Aug 2018, 11:19 am   #69
ChrisMarsden
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Default Re: Beam Echo Avantic SPA11 restoration. Help please!

Primary side of OT on both channels have a very similar resistance; around 380 ohms. I measured with multimeter at the points indicated (red dots).

Is this ok?
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Old 11th Aug 2018, 3:47 pm   #70
ChrisMarsden
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Default Re: Beam Echo Avantic SPA11 restoration. Help please!

It's alive!

It sounds great. No hum. Very little crackle from the pots, except as predicted a little from the 'balance' pot. I very happy and not a little surprised.

I found the 100W bulb in the spare room ceiling lamp in the end! Am I safe to remove it now or should I run for a while with it in place? Once I remove the bulb from the circuit am I likely to see any issues?

Thanks for all the help, so far!
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Old 12th Aug 2018, 4:23 pm   #71
ChrisMarsden
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Default Re: Beam Echo Avantic SPA11 restoration. Help please!

I removed the limiter and listened for 1 hour. The amp has a great sound. I'm pleased.

Next steps are get the Power transformer back in and correctly fused and earthed. The original 'mouse trap' fuse will be added back just for looks. I'm using a 500mA quick blow right now.

I'll also add some of my scanned diagrams, photos, (maybe a parts list) and notes once I'm completely sure everything is good - for future SPA11 restorers.

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Old 13th Aug 2018, 6:50 am   #72
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Default Re: Beam Echo Avantic SPA11 restoration. Help please!

Good work Chris. A LL is used to limit the current to the DUT (device under test) it also gives an indication of any shorts and other problems. It should glow bright at SW on then go to a dull orange, if it remains bright, you have a short or other fault.

One thing, always make sure you have a load connected with valve amps, be it a speaker or dummy load , IE resistor.

Glad your enjoying it, Andy.
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Old 13th Aug 2018, 8:40 pm   #73
ChrisMarsden
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Default Re: Beam Echo Avantic SPA11 restoration. Help please!

I need some advice on a power switch for the amp as it doesn't currently have one. The original was integrated in the volume pot that was replaced long before i received it.

One ideal location for a switch is on the back where the 'AC outlet' socket resides. it a small rectangular hole at 19mm x 9mm. I have a 240v 4amp switch that fits nicely. Its a spst. Will this be safe and within tolerances for the amp?

I also have a double poled toggle switch which I'd love to use but it would require modification of the case as it requires a 12mm diameter hole and it is rated at 10amps and looks the part to!

However, I'd rather not drill or modify the case if possible. what do you think about using the 4 amp switch?
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Old 19th Aug 2018, 4:54 pm   #74
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Default Re: Beam Echo Avantic SPA11 restoration. Help please!

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A good 7 hour listening session today. The Avantic is re-built and re-assembled and sounds pretty good.

I went with the miniature 4 Amp switch in the end - made a small panel out of aluminium so it fits perfect in the AC outlet slot with no cutting or drilling of the case.

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One area I didn't touch is the bass/treble circuit. The polystyrene caps look original (60 years old). I mention as I think the mid-range is a little flat compared to my other valve amp. I'll have a few more sessions before I replace them.
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Old 19th Aug 2018, 5:09 pm   #75
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Default Re: Beam Echo Avantic SPA11 restoration. Help please!

Polystyrene capacitors are actually among some of the most stable. If you can it might be worth extracting a few and checking their values with a dependable meter. You might find that they're no different from whatever you'd replace them with. In my experience the major problem with polstyrenes can be their physical fragility. When it comes to desoldering them it's all too easy to melt the plastic and/or inadvertently pull a lead out of the cap body. It's worth being very gentle with them.

As far as frequency response goes, 'flat' is normally what people aim for, and that's usually easiest to achieve in the middle of the spectrum. If your mid-range sounds flat then I guess that's the same as saying that the extremes (bass, treble) are either boosted or cut. That might well be the case if the tone control components have drifted. Can you find settings of the controls where the whole spectrum sounds uniform ?

Cheers,

GJ
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