1972 Frankfurt radio 8ohm+ speaker 4ohm resistance

[911MRP]

You don’t specify which “period correct” model Frankfurt as there were several on market around 1972 but if it helps this so the original spec for the Frankfurt US from among my factory references





Of course we don’t know what the previous owners or person who sold it has done to the unit that led to the speaker impedance advice they gave. If it were me I’d want to ask them what they know and why they advise 8 specifically.

Steve

[camarilla]

Hey steve that’s really interesting thanks for sharing. I’ll need to check with the seller (vintageblau). I was told that 8 ohm is what the original specification was but it seems like that wasn’t the case according to the hand book. I’ll investigate and report back.

EDIT: Steve what’s the date for that manual? Here’s Ingo’s response from vintageblau:
“1974 is the first year of four ohm. Before that radios are eight ohm. The change in speaker plug configuration shows this as well. Do you have the banana plug style with both plugs the same shape. Later they became pin and spade.”

I am no expert in radios but I trust Ingo as he deals with them day in and day out…

[911MRP]

I recommend you follow his recommendations. As others have explained the sellers recommendation is the more is conservative approach.

Without the specifics of which year an version Frankfurt you have based on seven digit model code and actual serial number it is impossible to have a fact based discussion. Also even if know all that the unit might have been modified.

I would for general interest be curious to see the label on the side of your actual unit showing the name, seven digit code and the serial number. If no photo al least share what label shows. Those specifics would better inform the topic. Likely among my many period factory binders I’ll have the original factory technical paper that Blaupunkt published for use by its professional service/ repair network ( not end-consumers) back in the day. I expect as a market leader in Europe Blaupunkt were pretty good at version control of such technical papers issued to that repair network community at least within constraints of binder/ paper publishing.

Their period papers I’ve looked at usually refer to a seven type number that can be decoded to show year that type of radio was first introduced to market. The serial number usually has an alphabetic prefix that gives the year the instance of the radio was made. Sometimes the papers give a serial number which the papers apply from if a spec/ engineering change happened to model. So should be possible to narrow things down if you share the label the datapoints. Frankfurt was in production many years, some years had variations for America stereo mono. The seven digit number and serial number are the key to original spec. While the knowledgable can tell it is easy for those less familiar to get confused without those numerical identifiers.

Always open to learn but must say I was surprised about what your expert said regarding the date of impedance change by Blaupunkt but nevertheless you should follow what supplier expert recommends if he knows and supplied the particular unit.

Steve

*PS one further point … could it be his comment is in reference to a multi speaker e.g. pair, three or or two pair driver installation where depending on how their wiring is configured ( serial parallel etc ) the impedance is affected ?

[camarilla]

Agreed.
It’s a 1972 US Frankfurt Mono radio model that’s unfortunately all the info I have on hand right now. Ill see if I can get a picture of the sticker and I’ll post it here. Seller refurbished the radio so I trust he’ll understand the electronics more than me. He might have modified the internals but I wouldn’t see a reason why he would have.

[911MRP]

The reason I’m surprised is the paper I posted is to the best of my knowledge for 1972 Frankfurt US mono was 7.632.627 from 0225001. The speaker impedance spec is shown circled. It is Blaupunkt original document from the binder on my shelf — the one on shelf with the 1972 sticker.



My understanding is the “2” in the fourth position of the 7.632.627 indicates that model was first on the market from 1972.

Not clear if 1972 in context of decoding their number is calendar 1972 or Blaupunkt own manufacturing year which might not align to calendar year (maybe rather like Porsches manufacturing year changeover doesn’t align to calendar year?). The serial number prefix on label along with the 7 digit code will give more of a guide to when your specific unit was made. It could be a for model year 1972 Porsche was built in latter part of calendar 1971 so possibly received an earlier version of the Frankfurt mono US spec. I have papers for earlier one too. My understanding as before is the “1” in the fourth position of the 7.631.627 indicates that model was first on the market from 1971 and was applicable per the “valid from number until superseded by mode and “valid from” shown in uppermost picture.



It could be there are other papers in my binders beyond the two pictured but they seemed the most pertinent to attach from your general description of your radio

I’d be interested in the specialist explanation why (particularly if it turns out one of the paperwork examples I attached corresponds to your radio model and serial range), why he requires 8ohm speaker when Blaupunkt paper gives the particular range shown in the red or green circle? Something doesn’t quite tally between what he says about 8 and 4 ohm change at least on evidence of this example of one original manufacturer technical binders ?


In light of the datapoints attached I am not convinced based on Blaupunkt data circled an 8 to 4 ohm change date coincided with the later speaker cable terminals. Querying what appears to be a quote from your expert? Especially as a quick glance at the European spec Frankfurt paper (not pictured as not so relevant) showed same range to these US model ones I’ve circled … is he saying the original Blaupunkt technical papers issued to repair and service network around 1971 and 1972 were incorrect when showing the 4-5 ohm speaker impedance datapoint? Or maybe he modifies them ?


So looking at these examples original spec papers which seem likely to bracket the US mono Frankfurt versions on market around time in question I’m obviously surprised at what your seller expert stated (assuming those are his views in quotation marks ?) about 8ohm impedance But only the seller know the specifics of your actual unit so presumably has a reason for what speaker impedance he says is required even if that seems different to what it was on these Blaupunkt papers whe unit was new. Maybe your unit doesn’t correspond to either of the examples — until know the numbers hard to be confident we aren’t at cross purposes. Enquiring minds now intrigued so want to know why he has this view which appears to suggest he thinks that it was a 8 vs 4 ohm blanket change later around 74 when much of dance had a facelift but these example OEM equipment suppliers datapoint I’ve attached seem to show otherwise. Hmm?

Having said all that, I’m not a radio specialist just have a hobby interest so best to follow your seller / specialist advice especially as it is more conservative choice and he knows the particular unit. Always open to learn from experts especially who can provide evidence

HtH

Steve

Was your Blaupunkt Frankfurt US AM/FM M-453 on its COA or other paperwork — what is production date of car if it had factory M option?

[camarilla]

Hey steve. Wow! Lots of info. Sorry, have been absolutely slammed with getting ready for a trip.

I need some time to go through your post. If helpful, I emailed Königs Radio and they were also surprised that the speaker they sent me is not compatible with my radio. Will get back to you on this

Here’s a pic I managed to snap of the inside sticker.

[911MRP]

Label helps we know what it is or at least was unit we when new. Had a quick look didn’t see the exact model in my factory binders but didn’t really look too carefully. However I did immediately come across this non US Frankfurt technical paper which gives steps of alignment procedure. It is Frankfurt 7639600 see the step at bullet point 2. It is referencing the speaker impedance for alignment procedure. Not saying is same as yours just sharing what I came across for general interest. I wonder how different the contemporary Frankfurt non USA version spec was to yours except for the ability to go upto 108 vs 104 on FM range to suit NA region’s reception. Maybe the Frankfurts had some commonality?



Or you can always look it up in this link , rather like online PET not as satisfying to use online stuff as having original factory printed binders and content but can be handy for a quick read — sometimes the content a bit of an eyesight test as uses scanned images:

https://www.radiomuseum.org/dsp_gues...plan_id=464262

I have to say I am with your speaker supplier at being surprised at 8 ohm speaker impedance requirement but only your radio seller knows the specifics of what it was he sold you.

Steve

Steve