"Expert" soundbox restoration

[streetmechanic14]

I'm in need of "Expert" advice:
(1) Is special material necessary for new diaphragm gaskets or will the ordinary Victor/HMV Exhibition tubing do the job? Is its only job to provide an air seal (as in an Orthophonic) or does its resilence play a more active part in the results I can expect (as in an Exhibition)?

(2) Does a good restoration include replacement of the small washers under the springs? What is their purpose? Is resilience important here too?

(3) Are the rectangular orange rubber cushions actual Ginn parts or might the former owner have been experimenting? They're hard as rocks; if they do something useful, presumably I'll have to replace them.

(4) Any idea what revisions or adjustments the 1940 letter (from David Philips) refers to?

_Dave

[Steve]

To your first question I'd answer yes as you will not get the optimum performance using the standard white tubing. I use a light beige colour tubing which I recall is used in medical supplies. I'm not sure what it's intended use is but it is very soft and works perfectly. The white Exhibition replacement tubing is too firm for an Expert soundbox IMHO.

Q2. answer: Yes/Yes
Q3. answer: Sort of
Q4. answer: No, but the Dynamic was the name given to the 4-spring soundbox so I believe it's just a reference to that.

[Steve]

I'm in need of "Expert" advice:
(1) Is special material necessary for new diaphragm gaskets or will the ordinary Victor/HMV Exhibition tubing do the job? Is its only job to provide an air seal (as in an Orthophonic) or does its resilence play a more active part in the results I can expect (as in an Exhibition)?

(2) Does a good restoration include replacement of the small washers under the springs? What is their purpose? Is resilience important here too?

(3) Are the rectangular orange rubber cushions actual Ginn parts or might the former owner have been experimenting? They're hard as rocks; if they do something useful, presumably I'll have to replace them.

(4) Any idea what revisions or adjustments the 1940 letter (from David Philips) refers to?

_Dave

To your first question I'd answer yes as you will not get the optimum performance using the standard white tubing. I use a light beige colour tubing which I recall is used in medical supplies. I'm not sure what it's intended use is but it is very soft and works perfectly. The white Exhibition replacement tubing is too firm for an Expert soundbox IMHO.

Q2. answer: Yes/Yes
Q3. answer: Sort of. They were likely applied by Expert, possibly during a regular "tuning" exercise but they are not unique materials per se.
Q4. answer: No, but the "Dynamic" was simply a reference to the name given to the 4-spring soundbox, so I believe it's just a reference to that.

[Orchorsol]

I'm in need of "Expert" advice:
(1) Is special material necessary for new diaphragm gaskets or will the ordinary Victor/HMV Exhibition tubing do the job? Is its only job to provide an air seal (as in an Orthophonic) or does its resilence play a more active part in the results I can expect (as in an Exhibition)?

(2) Does a good restoration include replacement of the small washers under the springs? What is their purpose? Is resilience important here too?

(3) Are the rectangular orange rubber cushions actual Ginn parts or might the former owner have been experimenting? They're hard as rocks; if they do something useful, presumably I'll have to replace them.

(4) Any idea what revisions or adjustments the 1940 letter (from David Philips) refers to?

_Dave

To your first question I'd answer yes as you will not get the optimum performance using the standard white tubing. I use a light beige colour tubing which I recall is used in medical supplies. I'm not sure what it's intended use is but it is very soft and works perfectly. The white Exhibition replacement tubing is too firm for an Expert soundbox IMHO.

Q2. answer: Yes/Yes
Q3. answer: Sort of. They were likely applied by Expert, possibly during a regular "tuning" exercise but they are not unique materials per se.
Q4. answer: No, but the "Dynamic" was simply a reference to the name given to the 4-spring soundbox, so I believe it's just a reference to that.

Q1. Similar to Steve (I think) I use a light beige natural rubber tubing which a lot of EMG & Expert afficionados use. I find it superior to the white silicone rubber tubing in all soundboxes. There are many different measurable physical properties of rubber compounds which can be difficult to relate directly to performance in a given application, but I believe the resilience of natural rubber (specifically this means rebound or bounce characteristics) as well as low hardness is key. The tubing I and others use is supplied for vintage bicycle tyre tube valves. I don't know exactly how that relates to Steve's surgical tubing.
Q2. Agreed, yes often replacements are needed, but originals seem to have been leather, which if still supple and not crushed too flat, I leave.
Q3. Found between the needle pivot bar and the body, rubber or cork pads? Everyone I know leaves these out. Always.
Q4. Agree with Steve. I wish we had their knowledge and tips passed down!
A few other brief tips - cut the gasket ends slightly oblique so they meet nicely - and slightly over-length making it a bit difficult for them to sit in position as you close the soundbox up - assemble with the springs gently holding the diaphragm in the 'null' position (quite tricky) - don't screw the two parts of the body fully together (some people put a rubber washer or a sliver of gasket tube in between on each of the screws). Tune by adjusting both the gap and the springs in small increments. Best performance is usually with everything at fairly low pressure (but ensuring airtightness). Others may disagree with some of the foregoing, but this is what maestro Ian Maxted taught me years ago!

[streetmechanic14]

Thanks for the very useful advice! Some more questions:

Might the purpose of the small washers be to provide a gentle locking action for the screws, gentler than would be possible if standard lockwashers were used. Lockwashers would have had to have been torqued down firmly and may have left the springs under considerable (and undesirable) tension.

My Expert Senior came with the two soundboxes shown in the attached image. Was the one on the left originally a two-spring which at some point was factory converted to four? If I'm right about that, it would be in line with Steve's interpretation of the word "Dynamic" as used by Ginn. The conversion was fairly rough- the two new spring screws were too long and have been coarsely chopped off (accounting for the scratches/file marks on the soundbox body).

Any suggestions about where to find appropriate gasket material would be greatly appreciated.

-Dave

[Orchorsol]

Might the purpose of the small washers be to provide a gentle locking action for the screws

Possibly, but I think the main purpose is soft cushioning and isolation from the body. The screws are not necessarily tightened as such.

Was the one on the left originally a two-spring which at some point was factory converted to four?

Without looking further, I don't think so... I'll dig out one of my Expert 2-springs tomorrow. There's something odd about both masks, especially the left hand one - but then many were modified by owners, often in an attempt to reduce weight (which personally I don't think is advantageous at all, especially with thorn and fibre needles).

[Steve]

Any suggestions about where to find appropriate gasket material would be greatly appreciated.

-Dave

For the sake of clarity the tubing I have used until now has been sold to me as bicycle valve tubing but I have some of this along with haemostasis tubing and I'm hard pushed to tell any difference between them:

https://ebay.us/m/HFXm4g

[Orchorsol]

Steve's source might be of good quality, I don't know, but some I've bought from China in the past has degraded quickly and shown darkened/hardened blotches (chemical bloom/degradation) in a year/18 months or so. I buy mine in ridiculously large lots from a cycle supplies wholesaler every few years. It's listed at £7 per metre on my website. Also available on eBay at higher price!

[Orchorsol]

Here are a 4-spring and 2-spring Expert from amongst mine.