Some of the TIPs were darlington pairs so that solved the gain problem. As for bandwidth, you didn’t want too much otherwise you have to contend with instability. Anyway what’s 20kHz compared with 1MHz. This is water under the bridge.
I have some GE tab transistors too.
I cannot argue too much (I can a little) with your math. But sometimes it is necessary to actually design and build an amplifier to appreciate the issues. I have not dived deeply into the design of bipolar transistor based audio power amplifiers. But I gather that the bandwidth of these is a limitation for that purpose. I think that the D44-D45 (and also look up 2SA2222) have much better gain characteristics although they may be less rugged. (Oh my darlington!) transistors give very high DC gain but I think they end up being pretty bad for a high quality audio amplifier. I bet someone on this forum has more experience with this…
You have to also recall the audio chain of that era. The cassette deck, the vinyl player, the FM station, the speakers were weaker links than the amplifier. Of course if you were an audiophile where money is no object you would not be DIY.
I have not had the urge to build audio amplifiers for decades. Off-the-shelf equipment now is better than my ears (almost anything is 
). Actually I don’t even need a lot of the touted “IoT” stuff. One of these days I’ll prefer burgers to gerbers. 
Edit: Found the 1973 catalogue of my local electronics shop and attaching the page listing the transistors available. Buying two pairs of power transistors was quite a chunk out of my schoolboy pocket money. My brother-in-law built his amplifier with 2N3055s for the power stage. But then he was an EE and I was just a kid.
1973-transistors.pdf (185.8 KB)
Edit 2: And while we are at it, here is a page from another supplier from about the same time listing their MHTL and MDTL offerings. Other pages listed the 7400 and 4000 series.
motorola-mhtl-mdtl.pdf (90.8 KB)
Prices look “ouch”.
What currency, if I may ask?
I remember 2N3055s at about AU$3.00 sometime in the 70s.
Ringgit (about 3 to AUD I think but I can’t be sure, it’s been 50 years).
I spent a lot of time in the early/mid 70s messing with 4000 series. As I recall most were between 1 & 2 AU$.
Sometimes you could buy gates and occasionally flip-flops for 50c on special, but never anything really cool like counters and decoders.
I also remember buying stuff from the US by mail order. Stuff was cheaper in the US and the currency conversion then was about 1 AU$ = 1.2 US$… that was where my first dim and horribly expensive red LEDs came from.
I bought stuff by mail order too, for the same reasons. Also from the UK. No Internet of course, the sellers had ads in hobby magazines. And some grab bags which were seconds and lucky dip. The DTL ICs came from Bi-Prepak in UK. It took me nearly 50 years to put them to use. 
Funny how one recalls some things.
I remember buying, but I just have no clue as to how I paid for them. I don’t think we had credit cards in those days in Australia.
I suppose I must have sent a bank cheque with my order by real mail and then waited a month or three for the stuff to arrive. I just don’t remember. 
Postal order by mail most likely.
You’re probably right. I’d forgotten all about them. It certainly was a different world then.
As for why the directive and the function of the transistors in question… that was about 30 years ago.
These were the main boards in a series of drive-through intercoms and were already designated “old style” as the current production version was completely different (and only belatedly respun into an SMT version a few years ago).
I think they were used more for some kind of switching function as the audio section of these boards used a 5-pin TO-220 (TDA2002 or similar). It seems to me they had a few where the encapsulated portion had split off the base. They changed vendors, but chose to deal with the ones already in the field through the spares program rather than deal with a recall.
Are any RTL or DTL still sold anywhere?
About TO220. To me it has been enough that pins go to 2,54mm grid, and you better check how your device is connected
Except for collectibles I doubt it. Any equipment that used those chips would have been decommissioned decades ago. Probably even the classic TTL (pre-LS) are rare too.
I sort of agree. I have not heard of popular attraction to those devices (as opposed to vacuum tubes; you probably know that many people like vacuum tube audio amplifiers.) I think that the popularity of RTL or DTL was shorter lived than that of vacuum tubes or CMOS or TTL.
Digital is fairly standardised in function. RTL was Really Terrible Logic with poor fan-out but it was all they had to work with. TTL was a logical step up from DTL, if you squint you can see the diodes in the multi-emitter transistor. Today’s CMOS based TTL bears little internal resemblance to the original family.
Popular is the wrong word because the populace couldn’t afford those parts. They were expensive chips used in professional equipment, see the prices in the catalogue I posted earlier.
Also people get nostalgic over the sound of old audio but who does that with digital logic? People usually remember the look, like VFDs, nixies, Panaplex. And some people refurbish classic digital clocks.
If one had to make old equipment work again one could replace old digital logic with a MCU, FPGA, or CPLD, annoying the purist retro-refurbishers.
How about Mom and Popular?
Mainly I am referring to how many were manufactured or purchased or used in equipment. I am guessing that those numbers were all relatively small compared to even TTL. But the average consumer would have been unlikely to own electronics which contained TTL logic. Maybe some people had TTL illogic?
Here I went to DigiKey and first searched for “TTL”; selected “gates and inverters”. When I narrow it down to 7400 series (I think that was the dominant family of TTL) then 547 listings become only ONE.
But this could be due to the effect of the plummeting prices and widespread availability on the numbers of equipment designed with that family. Designers don’t ask is TTL getting more songs in the hit chart than DTL, they just go with whatever does the job for the price, reliability, complexity, power consumption, etc. etc. Eventually DTL was no contest for TTL with its variety of functions. You could still reuse your DTL skills as both are current sinking logics. So the relative numbers don’t tell you much except that technology has progressed.
I’m guessing that stuff is so old there just was not a big market for it. A bunch of companies made mainframes or other industrial type stuff.
I’ve got a suspicion that digital logic made an explosive growth in the early '80-ies when the home computers became popular. More people getting to know computers may also have helped to grow in industrial branches.
BTW here’s a case of spectacularly unfortunate timing for a design. In 1972 the British magazine Practical Electronics began publishing a 11 part series for a TTL desk calculator. About 2 parts in, the TI all-in-one calculator chips were released, obsoleting the TTL design.
I’d go for the mid Seventies when the manufacturing prices of all components electronic started to fall through the floor. Hobby electronics became affordable and industry for domestic products first started to consider replacing electro/mechanical devices with electronic versions.
It sort of took 'till the Eighties to see the effect with domestic appliances as Paulvdh suggests, but industry takes 10 years to adopt radical change.
Nahhh,
I think it is the accessibility. Anyone who considers themself an authority can fix and maintain the old stuff. A $10 100W soldering iron and a $5 multimeter will get you a license. You can almost see a leaky paper capacitor or “gone high” resistor and you only need a cloth to polish the glass envelope of a valve… doesn’t even need unsoldering.
The new stuff is little black rectangles on green boards, everything glued or soldered in place. It needs specialist soldering equipment, not to mention: how do you diagnose a fault?
It is well out of the realms of Joseph Bloggs.
On top of that, the price keeps dropping!
Who fixes a TV or computer monitor anymore?
I still have a 1984 Yamaha CD player deck. It is so old it doesn’t have a remote control.
It cost $750 in 1984. It is full of little black boxes on brown boards. I bought a dvd/cd player with remote for my shed for $25 new 5 years ago, and it is not very full of similar black boxes on a more attractive green board. Why bother trying to fix the old one, if I could get the parts?
Domestic electronics has generally become unserviceable and the public conditioned into buying the latest and greatest.
Sometimes I worry about how many perfectly good surface mount resistors and capacitors have been consigned to landfill.