Collecting: Finding and Buying One

CRT calculators are hard to find, and harder to find working. They were expensive office and laboratory machines; most were scrapped when cheaper calculators replaced them; radio amateurs took many apart for their tubes; and their weight keeps them out of the ordinary parcel trade. This volume covers why searches come up empty, what to search for, where to look, what they cost, and what to check.

9.1 Why searches come up empty

A search for “CRT calculator” finds almost nothing for sale, because sellers rarely know or say that the display is a cathode-ray tube. Listing titles seen in sales records include “Vintage Friden 130 RPN Calculator Working”, “Vtg Friden 132 Electronic Calculator EC-132 rare collectible Local Pick Up”, “Vintage 1963 Friden 130 Electronic Calculator”, “Vintage SCM Cogito 240 SR Rare Calculator Adding Machine”, and, at an auction house, simply “4 Electronic Calculators” for a lot that held a Friden 132. The machines are listed by model number, as “calculator” or “adding machine”, or in mixed lots.

9.2 What to search for

Save searches for every model name, with alerts:

• Friden: friden 130, friden 132, EC-130, EC-132, EC130, EC132, friden electronic, singer friden, friden 1160, friden 1162, friden 1166
• Hewlett-Packard: hp 9100, 9100A, 9100B, hewlett packard calculator 1968, and the peripherals 9120A (printer) and 9160A (card reader), which turn up separately and lead to the machine
• SCM: cogito, cogito 240, marchant 240, smith corona marchant electronic
• Wyle: wyle, wyle scientific, WS-02
• Victor: victor 3900, philco 3900, philco ford 3900, victor 14-321, victor 1400
• Others: busicom 202, busicom 207, monroe 820, descal
• General: crt calculator, cathode ray tube calculator, transistor calculator, oscilloscope calculator, vintage computer 1960s, delay line, germanium calculator
• Misspellings: fridan, frieden, freiden, cognito 240, hewlet packard 9100

On eBay, search all categories with “include description” ticked. The main categories are Vintage Calculators (category 58042) and Other Vintage Computers (4193); business-equipment and science-collectible categories catch a few more. Search eBay.de and eBay.co.uk as well as eBay.com: European 9100Bs have sold cheaply.

9.3 Where to look

In order of how much they have produced:

1. eBay, worldwide, with saved searches. Every priced sale found for this series came through eBay.
2. The HP Museum forum (hpmuseum.org/forum): its for-sale threads are where 9100 owners trade, and a “wanted to buy” post there reaches the right people.
3. Rick Bensene and the Old Calculator Web Museum (oldcalculatormuseum.com). He answers email, knows where machines are, and trades; the Old Calculator Forum on Google Groups is the collectors’ list.
4. The classiccmp mailing list (cctalk), where EC-130s and 9100s have been offered, given away and repaired.
5. The Vintage Computer Federation: the forum’s for-sale and wanted sections, and the consignment rooms and swap meets at the VCF East, West and Southeast festivals.
6. Auction aggregators with alerts: LiveAuctioneers, Invaluable, HiBid and Proxibid, plus Bonhams’ history of science sales and Auction Team Breker in Cologne. Lots are often mislabelled and come from estate sales.
7. Hamfests and electronics flea markets. Radio amateurs owned these machines, if only for their tubes.
8. University and government surplus, and estate sales: GovDeals, university surplus stores, EstateSales.net, ShopGoodwill. These were laboratory machines: one 9100 and plotter were rescued from a skip behind the University of Iowa’s physics building in 1989, and the Amsterdam university museum’s Friden 132 came from a medical physics laboratory.

Reddit’s r/calculators and r/vintagecomputing, the Facebook calculator groups and Craigslist or Facebook Marketplace (worth a saved search, because of local-pickup sales) have produced less. WorthPoint holds records of past eBay sales and is worth a subscription when you are about to bid.

9.4 What they cost

There are very few sales on record. Prices below are from sales records and forum reports; those marked unconfirmed come only from search-engine extracts, because the pages themselves could not be read.

Table 1 — What they cost

Machine	Price	What it was	When	Source
Friden 130	$559	sold, working (“CRT has dots on the right”)	probably about 2017	eBay, via PicClick (unconfirmed)
Friden 132	$1,299 or offer	asking, working, local pickup	about 2025	eBay (unconfirmed)
Friden 132	$600–800	auction estimate; hammer price not shown	December 2018	Bonhams, New York
HP 9100A with 9120A printer and 9160A card reader	$2,125, one bid	sold	not dated	eBay, via PicClick (unconfirmed)
HP 9100A, working	$3,000–4,000	collectors’ estimate	February 2023	HP Museum forum (unconfirmed)
HP 9100A	$2,500–3,500 or more	collectors’ estimate	March 2024	HP Museum forum (unconfirmed)
HP 9100B, two not shown working	€400 and €350	sold, one with a 9101A memory unit	February 2023	Germany, reported on the HP Museum forum (unconfirmed)
Wyle, Victor 3900, Busicom, Cogito, Monroe 820, Victor 14-321	no sales found

A working Friden 130 or 132 seems to sell for roughly $500–1,300; an HP 9100 from a few hundred euros, untested in Europe, to $2,000–4,000 working in the United States. The rarer machines effectively have no market price because they almost never appear. The Old Calculator Web Museum’s own wanted list includes the Wyle WS-01, the Cogito 240, the Victor 3900, the Busicom 202, 207 and 2017 and the Monroe 820A, a good measure of how scarce they are.

9.5 Rarity

• Findable, with patience: Friden 130 and 132 (about 34,000 made between them), the HP 9100A and B (especially in Europe), and the Friden 1162 and 1166 (lighter and later; the 1166 was made in the largest numbers of all).
• Rare: SCM Cogito 240 and 240SR, Monroe 820 and 820A, Victor 14-321 and 14-322.
• Very rare: Victor 3900 (a little over a thousand made, many scrapped), Wyle WS-01 and WS-02, the Busicom machines (mostly in Japan), the Romanian Felix CE 30 (fewer than ten known), and the Logicon (two to six made).

9.6 Before buying: a checklist

1. Ask for a video of it powered up, showing digits on every row of the tube. On a Friden ask for 13 nines divided by 1, which should take about two seconds; on an HP 9100, a division by zero, which should light the ERROR lamp.
2. Look at the tube for burn: shadows of digits or zeros that stay when the display changes. On an HP 9100 ask for a photograph of the getter in the neck of the tube. Silvery is good; white means the tube is cracked, and it is the one part that cannot be replaced.
3. Rust, liquid damage and infestation are the reasons the Old Calculator Web Museum rejects machines. Check that the bottom plate and its screws are there.
4. Are all the boards there, and original? Many Fridens were stripped of their tubes.
5. “Untested, never powered” is better than “powered and dead”. A machine switched on with a cracked tube or dried-out capacitors may have done itself further damage.
6. Extras worth paying for: the serial number (a Friden 130 from 8501 is a three-counter machine; earlier is four-counter), square root, the item counter, manuals, the dust cover, HP magnetic cards and peripherals.

9.7 Getting it home

These machines are heavy and their delay lines and tubes do not like shocks:

Table 2 — These machines are heavy and their delay lines and tubes do not like shocks

Machine	Weight
Wyle Scientific	about 50 lb
Friden 130 and 132	42 lb
HP 9100A and B	about 40 lb
SCM Cogito 240SR	39 lb
Victor 3900	24 lb
Friden 1162	24 lb
Monroe 820	14 lb

Many are sold for local pickup only. Collect in person where possible. Otherwise use a professional packing service, double boxes with plenty of foam, or freight. Bonhams marked its Friden 132 as an oversized lot.

9.8 A note on authenticity

These machines are not reproduced or faked, but they are often mis-described. A “Friden 130” may be a mechanical or Nixie Friden; a “CRT calculator” may be a later Nixie or vacuum-fluorescent machine with a green display. The model volume’s last section explains how to tell a CRT display from the others at a glance.

Sources

The documents behind this series are in the Reference Library. The main web sources:

• Rick Bensene, The Old Calculator Web Museum: exhibits and specifications for every machine in this series. https://www.oldcalculatormuseum.com/
• Nicholas Bodley, “The Friden 130: the world’s second electronic calculator”, and Dick Ahrens, “My life and times at Friden”, both on the Old Calculator Web Museum.
• Serge Devidts, Calcuseum: the CRT-display listing. https://calcuseum.com/
• DoPECC calculator collection. https://dopecc.net/
• The HP Computer Museum (hpmuseum.org and hpmuseum.net) and the HP Memory Project. https://www.hpmemoryproject.org/
• Jürgen Keller, hp9100.info: HP 9100 documents and repair videos. https://hp9100.info/
• Trinity College Dublin, School of Computer Science, computer collection catalogue.
• The Computer History Museum and the Smithsonian National Museum of American History catalogues.
• Wikipedia: “Friden, Inc.”, “Victor 3900”, “Hewlett-Packard 9100A”.
• The classiccmp (cctalk) mailing list, the Vintage Computer Federation forum, and the HP Museum forum.