HK Citation III History Questions?
The recent discussion here about how to align the Harman Kardon
Citation III tuner brought back memories of my youthful desire to own
one when they first came out. I was impressed by all the bells,
whistles, and knobs the tuner had, probably more than any other tuner
at the time. Fortunately I knew better by the time I was able to
upgrade from my Heathkit FM-3A and was wise enough to make a better
choice than the Citation III.
Still my curiosity about this old tuner has been roused and I hope
there is a Harmon Kardon expert in the group that can answer a few
questions for me.
1. What was the date of the Citation III's introduction, and what was
the initial list price of the kit?
2. Looking at the schematic I noticed an unusual feature I never
noticed before and which seems strange to me. A Nuvistor and half of
an ECC85 form a cascode RF amplifier, nothing too unusual there,
however the second half of the ECC85 is used as a resistance coupled
RF amplifier between the cascode RF amplifier stage and the mixer
grid. This is something I have not seen done in other tuners and it
has me wondering whether it helps or hurts performance?
I remember that at least one of Harman Kardon's factory wired tuners
at the time used an RF-IF "cartridge" which appeared externally
identical to the RF-IF "cartridge" used in the Citation III, except
that there wasn't the extra Nuvistor RF stage on the main chassis.
It occurs to me that the odd resistance coupled RF stage in the
Citation III may have been the result of a desire on the part of HK
to use an existing RF-IF "cartridge" in Citation III with only minor
wiring changes in the RF amplifier, which left them with an extra
triode section when the first triode was replaced by the external
nuvistor, and that they decided to press this leftover triode into
service as an additional RF amplifier stage in the Citation III
version of the RF-IF "cartridge". Does anyone know what HK tuner
models may have used a similar RF-IF "cartridge"? I would like to
see what the original circuit of this HK RF-IF "cartridge" looked
like without the added external nuvistor stage.
3. Are there any web sites devoted to Harmon Kardon tube audio
products that would show me their product lineup from the late 1950s
and early 1960s? I have done some Googling but have not come up with
Hi John;toggle quoted messageShow quoted text
Good questions, which I don't have good answers to, but will make a comment or two.
There are 4 gangs in the Citation III tuner, in a rather odd mechanical arrangement I had never seen used before, or again. Normally most 4 gang tuners use a tuning cap that has 4 gangs arranged on a single shaft to make things simple.
In the HK Citation III, there are 2 tuning caps, each with 2 gangs, mechanically coupled with 2 small gears. Like you, I can see no other reason to do it this way, other than they had a pile of the 2 gangs units in stock. Synchronization of the 2 caps using the gears would be a little messy during manufacturing or service.
The first 2 gangs are tuned after the antenna input, before the 6CW4 nuvistor RF amp stage. Having 2 gangs before the amp is felt by many to be good practice, it will likely also affect the sensitivity for the negative.
Also, you did not mention anything about the use of the two 6BN6 limiters in the Citation III. From what I recall, there was only one other series of tube tuners to use two of them, the Scott 310.
--- In FMtuners@..., "bta_50g" <byrnsj@...> wrote:
--- In FMtuners@..., "newaag" <bob@...> wrote:
Interesting, I have never seen a Citation III up close and personal
so I didn't realize that the gangs were arranged in this way. I
found a photo of the chassis without the front end shield in place in
an old Audio magazine and only two of the gangs were visible above
the chassis so I assume that the other two gangs are under the
chassis as part of the "cartridge"? This new information changes my
speculation about wiring modifications to an existing RF-IF
'cartridge" design for use in the Citation III, it now seems more
likely that the "cartridge" was not modified for use in the Citation
III and that in its original application it was used as a two gang
front end with a grounded grid RF amplifier stage, the RC coupled
final RF amplifier stage is still unusual, perhaps even more so if
this new speculation is correct.
Split tuning gangs are not unheard of, the famous Western Electric
10A AM radio receiver used a pair of three gang variable capacitors
mounted end to end with a right angle drive to the front panel to
create the equivalent of a six gang tuning capacitor. I also have a
chassis module from what looks like it might have been part of a
military audio oscillator from the late tube era. It includes two
two gang variable capacitors one of which has a shaft extending from
each end. The shaft on one end is coupled to the second variable
capacitor to form a four gang unit and the shaft at the other end
serves for tuning in the normal fashion.
The first 2 gangs are tuned after the antenna input, before the 6CW4 nuvistor RF amp stage. Having 2 gangs before the amp is felt by many to be good practice, it will likely also affect the sensitivity for the negative.The Citation advertising literature mentions the two transitionally
coupled filters in the antenna circuit. I agree about affecting
sensitivity "for the negative" but it is interesting that the
advertising literature claims that the Citation III was the most
sensitive FM tuner available at the time.
Also, you did not mention anything about the use of the two 6BN6 limiters in the Citation III. From what I recall, there was only one other series of tube tuners to use two of them, the Scott 310.I didn't mention the two 6BN6 limiters because I didn't consider them
particularly note worthy. There are a few other FM tuners with two
6BN6 limiters, I think the National Criterion may be an example, the
H.H. Scott 310 series is not an example. One thing I don't like
about the Citation III is that it only has three IF filters while the
Scott 310 series tuners have four IF filters. The Scott 310s have
three IF amplifier stages followed by a single 6BN6 limiter which is
in turn followed by a normal 6AU6 saturation limiter driving the
Scott also tried a 6BN6 limiter in the original 350 stereo tuner, no
suffix, but the experiment seems to have failed as they quickly went
back the single 6AU6 saturation type limiter in the "B" model of the
350. I suspect that the two IF stages in the 350 may not have
provided enough drive for the 6BN6, it's interesting that Scott used
a "buzz" pot in the cathode circuit of the 6BN6 to maximize the AM
rejection as in a Television receiver, this also suggests marginal
performance as I have never seen another FM tuner with a "buzz" pot
in the 6BN6 circuit.
--- In FMtuners@..., "John" <byrnsj@...> wrote:
OK, John, help this technically-challenged list member. My "limited" (sorry) understanding about limiters is that they drive the signal into clipping so AM components disappear. And it seems as though the limiter is usually between a couple IF transformers. If I recall that part correctly, wouldn't the limiter stages tend to improve filtering like the previous IF stages?
--- In FMtuners@..., "sail_c2" <clcampbell@...> wrote:
I have never seen an FM tuner that operates as you describe with the
"limiter" between a couple of IF transformers, if you could cite an
example it would help? In the tuners I am familiar with the first
limiter stage is driven by the secondary of the last double tuned IF
transformer and the final limiter stage drives the detector. When
there is more than one limiter, as in the case of the Citation III,
the inter stage coupling between the limiters is usually a broadband
circuit of some sort and not a double tuned IF transformer, this
coupling generally takes the form of single tuned circuit which is
heavily damped by a low value resistor. In the case of the Citation
III the single tuned circuit is housed in a can that looks like an
ordinary IF transformer, and the damping resistor shunting the coil
in the Citation III is 8.2k Ohms. In the case of the H.H. Scott 310
series the coupling between the two limiters isn't even a heavily
damped single tuned circuit, the plate voltage for the 6BN6 first
limiter is simply supplied through a 6.8k resistor.
In very few, if any, tuners does the inter stage coupling between the
limiters provide any significant additional selectivity. Perhaps
someone more familiar with FM theory than me could comment, but it
seems to me that additional selectivity at this point would be of
little practical value, and may have theoretical disadvantages.
OK, no questions, just needed a old Citation III post to add this interesting item to gawk at - a brand new, still in the box Citation III Tuner for sale.
Not mine. Looks good for its age. Oddly, worth more apart than together?
That was my experience with a new-in-box (UNassembled) Heathkit AJ-15 FM tuner that I auctioned on eBay a few years ago.
I don't recall the precise final bid, but it was *several* times the average price for an assembled AJ-15!
I built one as a teenager when they were first introduced, and at the time, compared to my folk's console stereo, was a real hot rod.
I haven't been following eBay auctions lately, but for a time, NOS Heathkits were going for outlandish prices, compared to used, assembled versions of the same model.