Presto 1-C or 1-D differences?

[Stevie342000]

What are the differences in the Presto 1-C and the Presto 1-D? I have the manual/specification sheet for the 1-D but can not locate one for the 1-C.

I should think that there are few differences except the 10 years that separate there coming on to the market. The 1-C in 1939 and the 1-D in 1949. Ah research you see, on the broadcasting history site if you do a search you can find all the Presto advertisements in any given magazine.

The BBC had Presto 6N with 1-C on lease lend during WWII, you will find a whole new lot of references documents to trawl through which I posted on the reference section for the BBC documents there are lots lots more right up to about 1950 on disc cutting, there is a 1946 paper on one of the German tape machines which spells the writing on wall out clearly for disc cutter future. No BBC reviews of Rek-o-Kut strangely but there are reviews on Fairchild equipment. Suspect Rek-o-Kut did not have military contracts so was not available on lease lend, Presto & Fairchild both had links to the military and government.

[markrob]

Hi,

The only differences I could see were:

1. Different windings. The 1C came in 500 and 8 ohms. The 1D came as 500 and 15 ohms.
2. The damping material on the 1D was improved and shaped/mounted a bit differently.
3 Since RIAA was not in effect back in the 1C days, they would have selected the series resistor to mimic a turnover other than 500 Hz (e.g 250Hz was common back then).

Other than that, they appear to be the same to me.

Mark

[tragwag]

in my personal experience using both heads, the 1D's I've used are just much smoother in frequency response.
The 1C's are more "tinny" to me, and a lot less reliable. That's not to say they can't be compensated.
Also, anything that old that was created for such precision is obviously not as precise anymore, and heads age differently depending on how they were kept.

[Techie]

The Robert K Morrison book states that the 1D used a different damping material. The 1C used Viscaloid, which hardened with age. The 1D used Prestoflex, which was more stable over a longer period of time. They were both available as 15 or 500 ohms.

[Presto Repairs]

TECH DOCS OF THE PRESTO 1- C & 1-D Cutterheads

"The documented difference between the 2 models is a flat response difference of 2k - Attributed the the difference in damping materials used"

1-C Viscaloid "V" 1-D Prestoflex

Note: This is just what the tech docs say - I along with other members of this forum have seen these heads go beyond the documented responses...

I have personally had my 1-C reach 12k with no trouble (4k above the docs) & I have heard of some 1-D heads reaching 15k (5k above the docs)

[Presto Repairs]

The only other obvious difference worth noting between the 2 models is the placement of some screws and the serial numbers...

1st photo ( 1-C)

2nd photo (1-D)

[Stevie342000]

Thanks for the PM, other than the source data on the Presto 1-C from the Preservation Sound website, I could not find anything else. The best source would have been from the BBC but the file on the Presto 1-C is missing from their files. There is a research paper on the Presto 1-B, they did not rate the Presto equipment very much.

They were using the MSS designed by Cecil Watts who had done the research on lacquer discs, it gets murky here as he is stated as being the person who came up with the concept full stop. But my understanding is that Pyral held the patents, as Presto licensed it from them. But I do have a strong feeling that it was not patentable as there was nothing new in the concept and it was covered by earlier patents.

Cecil Watts came up with a cutting lathe for the BBC in 1933/4 after his initial experiments with lacquer discs he had three premises 2 of which were workshops in Soho (London) round the corner from his Shaftsbury Avenue flat and Office. He set fire to the Soho Workshops several times whilst working on the formula for acetate coated aluminium based discs.

The results of the BBC wartime research documents on the Lease Lend equipment from America was that it was not up to the standards of the BBC. Which resulted in them coming up with a new cutting lathe (Type 5 Recorder) as well as a portable version again built/designed by Cecil Watts to the BBC specification.

The Grampian feedback cutter heads were designed at this time as well by the BBC and built by Grampian. It was standard practice for the BBC to design the equipment and get a manufacturer under license to build it for them. Take the Coles microphones (Formerly part of STC - STC was UK division of Western Electric, the clue is in the name Standard Telephone & Cables and in the font used by STC), those are BBC designs from the 1950s which are still in production today.

The BBC had decided that if no one had the equipment that they needed or that could not be modified to meet the BBC standards, then they designed it themselves, they were at that cutting edge of technology, the microphone example shows that. The American equipment was not good enough it did not meet the BBC specifications, a lot of British firms fell foul of the BBC standard specification. There was a standard for everything e.g. it had to have certain frequency response, distortion output or if it was a tape recorder it had to conform to the standard for tape recorders. Oh yes and it all had to be 600 ohm input and output, which most domestic product was not it was nearly all high impedance although some of the amplifiers could and were modified e.g. Leak TL12 was used in LSU/10 modified for 600 ohm lines.

Recently there has been a couple of MSS cutter lathes for sale on UK eBay, one of them is a very late model and has been up for sale several times it comes with a late model amplifier as it uses KT88's in the cutting lathe amp and the cutting lathe (C/LED) will be 3 speed not 2 speed as the one which sold for £900 a week or so back this came with a couple of the tape machines PMR/1 the lathe was a PR/4C. I noticed that there was some documents with it as well, I contacted the seller and got a copy of what turns out to be the instruction manual as well as a sales leaflet listing the equipment range circa 1950 as there is no mention of the tape machines.

The PMR/1 was only in production from April 1951 to June 1952. The later models from the last date only sold 250 pieces of kit in 4 years. Whilst doing some searching on the BBC Type 5 recorder I came across this: http://bbceng.info/

Check out the bottom left hand side Technical Instructions http://bbceng.info/ti/ti_top.htm and if you go into the Pre-1960 documentation you will find this: Watts Disc Recording Machine.pdf at http://bbceng.info/ti/ti-pre-1960.htm. The documents are there for the driving amplifiers as well.

The difference between the MSS instruction I now have and the above technical instructions from the BBC are separated by 10 years and differ little. The MSS documents have the schematics for the amplifier as well which is essentially a single ended 6V6 Amp with a pre-amp/mixer stage at front. At some point I will scan the documents and upload them, along with other documents but currently I need a new scanner.

Both the BBC Type 5 and the MSS cutting lathes essentially the same thing were well thought out and needed little modification to cut MicroGroove Records other than a change of the leadscrew, it had outside in or inside out as standard and was able to cut from about 60 lpi to 150 lpi in the pre-LP era.

[Steve E.]

I have personally had my 1-C reach 12k with no trouble (4k above the docs) & I have heard of some 1-D heads reaching 15k (5k above the docs)

Indeed. My presto 1D cutterhead easily goes to 15K (down roughly 2db), at least in the outer inch of a 12" disc.

[EmAtChapterV]

When my 1D was working, it had a "hole" at around 14.5 or 15 kHz and the frequency response had peaks and valleys, but aside from the 15k hole it could easily be EQ'd flat all the way up to 22 khz and probably well beyond. (I never found how high the secondary resonance actually was.) You had to hit it hard above 12k and there wasn't much headroom, but it would do it.