Rogers Cadet MK3 using the Power Amp with a different Pre amp

[Farmerjake]

Hi All,
A while back I bought a Rogers Cadet MK3, it's the two piece pre amp & Power amp version. I've had it running for a couple of years now & love the sound but I recently saw a quad 33 in a hifi shop near me for fairly cheap & got me to thinking ....could I use a different pre amp with my Rogers power, would it sound any better/different, it would be an interesting experiment anyway.

The rogers has an umbilical which connects the two parts giving power to the pre plus the sound but it also the controls on and off to the whole setup. This is a 9 pin plug so wondering, is there a cable I can make that would allow me to try different pre-amps.

 

[Eli Duttman]

Look at the documentation. IMO, the hardest part of making the adapter cable will be sourcing the 9 pin plug. My guess is that a failed 9 pin mini tube will donate its base.

 

[Alllensoncanon]

This is a 9 pin plug so wondering, is there a cable I can make that would allow me to try different pre-amps.

In addition to the cable that allow an RCA plug, you will need to do a couple of mod.


1. Short circuit the AC power and use a power bar or add a power switch.
2. Either add a dummy load to the preamp power pins (draw the same current as a the preamp sectio so it could be hot) or change R16 such that the preamp stage of the tube won't be over voltage.

 

[Galu]

Hi Farmerjake - may I interject a word of caution?

It could be argued that the magic of the Cadet Mk3 happens within the control unit with its trio of (as rare as hen's teeth!) ECC807 valves.

The power amp section may be described as being competent, but I don't see it as an ideal test bed for alternative pre-amps.

From one Rogers owner to another, allow me to say that I'd be inclined to leave this classic combo, the sound of which you love, well alone.

 

[gingertube]

I'm with Galu,
For my clock radio to wake me each morning I run a FM Tuner into my Cadet III driving a pair of vintage Warfdales.

Tried it with Tuner in via the tape DIN socket which bypasses most of the preamp and via the Radio Input which passes through all of the ECC807 preamp.
Definitely sounds better when feeding through all the ECC807s of the preamp.

Lucky those ECC807 last forever. Last time I tried to get some, the price was such that a if working on commercial considerations alone, then the Cadet III would have gone in the bin and the ECC807 pulls sold off. In fact that was the state it was in when I acquired it (no ECC807s).

Cheers,
Ian

 

[Galu]

Definitely sounds better when feeding through all the ECC807s of the preamp.

Hi Ian!

I discovered exactly the same thing with my HG88 Mk3.

I feed my CD signal (suitably attenuated) into the 100mV tuner input. The CD sounds lifeless by comparison if connected to the less sensitive tape replay panel socket.

The HG88 Mk3 utilises four ECC807 valves and I thought that bypassing two of them by using the panel socket would sound best, but I was wrong!

My 807s are now 50 years old and functioning sweetly. Hope I never have to replace them as the going rate at auction is £100 to £150 for a single NOS valve.

 

[Farmerjake]

Hi All, thanks so much for all the information & replies.

So, looks like:

A) As suspected this would be a leap to far beyond my limited technical skills (I can solder but not much else!)

B) I should stick with keeping it original & preserving the sound as is. I'll maybe just buy the quad as a separate setup.

I have two 807's as spares I chanced across not long after buying the amp & snapped them up for £40 for the pair so all good for what sounds like a lifetime of listening.

I generally listen to vinyl but do have my aux cable running through the tape input so thanks for the advice on that, i'll switch to the tuner.

@Galu & @gingertube any recomendations on speakers that pair well with the Cadet 3?. I currently have some Acoustic Research 4XA which sounded great with my Sansui AU101 amp but less so with the Rogers.

 

[Galu]

Both the AR-4ax and solid-state Sansui AU-101 hail from 1973 and would have been a good match electrically.

The speakers may not be as well controlled when powered by your mid to late 60s valve amp. Factors like damping factor, maximum undistorted amplifier power and speaker sensitivity come into play here.

The sensitivity of the 4xa is quoted on this site AR Speaker Specifications as 86dB.

There can be little doubt that contemporaneous speakers of a higher sensitivity would better match the low powered Cadet amp.

It appears that Ian uses Wharfedale speakers from the same era as the Cadet. I use full range, 12" Wharfedale RS12DD drivers (see attachment) which I purchased in 1969 along with my HG88 Mk3 amp. They are very sensitive and have a synergy with valve amps.

Are the foam surrounds of the AR-4xa woofers in good condition and has your Cadet undergone any renovation such as replacement of the electrolytic capacitors?

 

[Farmerjake]

Are the foam surrounds of the AR-4xa woofers in good condition and has your Cadet undergone any renovation such as replacement of the electrolytic capacitors?

The AR's are in great condition but like you say they don't match as well as they do to the sansui.

The cadet is all in original condition other than a while back had a hum & a friend replaced one of the resistors, It's on my radar to do when I feel confident enough soldering or have the money to pay someone to do a good job.

I use full range, 12" Wharfedale RS12DD drivers (see attachment) which I purchased in 1969 along with my HG88 Mk3 amp. They are very sensitive and have a synergy with valve amps.

When I saw your thumbnail I thought Oh My God I'm an idiot I saw a pair of these at a boot sale for £50 last year but then had a look around and it was the same as these: https://www.wilkinsons.tv/product/wharfedale-unit-4-hi-fi-speaker-kit/

(Probably still should have bought them!!)

Is there a factory built speaker that uses the RS12DD driver?

I also debated getting some Rega RS1 speakers as a friend has them with an old leak amp & they sound pretty good if lacking in bass slightly.

Thanks again

 

[Galu]

There's no factory built speaker that employs the RS12DD.

The Unit 4 is the kit version of the original Wharfedale Melton which was claimed to have a sensitivity of 89dB.

The Rega RS1 has a sensitivity of 90dB so would go loud on the end of your Cadet.

My Rogers HG88 Mk3 (big brother to your Cadet Mk3) sounded better than new after replacing the rectifiers, power supply and other electrolytic capacitors. The effectiveness of such components has improved over the past 50 years. This, however, is a job for someone with the appropriate knowledge, skill and safety awareness.

The voltages at various points in the circuit have to be measured and compared to those published in the manual before the amp can be given a clean bill of health.

 

[Farmerjake]

Had a quick look around for some drivers & found a pair of the rs8dd around 45mins from my house. Which I think are the 8” versions. Do you think these would perform well? they’re currently in some huge cabinets that are a bit tired so could have a go at building some new enclosures if I can find some suitable plans. My living room is pretty small anyway so they never go up too loud.

 

[Galu]

I assume we are talking Wharfedale Super 8/RS/DD (see attachments).

These would be the basis of a fun build.

They are very efficient (the magnets are the same strength as those on my RS/12/DDs) and work well in a 1cu ft (28 litre) enclosure.

I can supply the original Wharfedale cabinet plans should you decide to go ahead with the purchase.

Out of interest, what is the asking price?

 

[Farmerjake]

Yes, they’re the above. They’re asking 145 or offers & say they’re in full working order. They have 2 different cabinet designs. The pic below is the larger.

 

[Galu]

Here are the Wharfedale cabinet plans: https://www.diyaudio.com/forums/att...464673376-wharfedale-super-8-rs-dd-ccs-p3-pdf

Details of distributed port and reflex loading versions are given.

It is highly likely that the current enclosure for the 8" Super follows one of those versions.

P.S. Was composing this post while yours came in!

 

[Galu]

This pdf of a Wharfedale catalogue may be of interest. http://www.ajaudio.co.uk/Whafedale speakers.pdf

 

[Galu]

They’re asking 145

The price of the Super 8 was £7 way back in 1962 - that's equivalent to £147 now!

 

[Farmerjake]

Amazing!! Thanks so much, yes the other cabinet looks like it follows that plan but looks like it uses chipboard (See attached)

 

[Galu]

Will you be able to listen to these speakers before purchase?

Since you are interested only in the drivers, I suggest that they are removed from the cabinets prior to purchase so that you can inspect the cones from the front.

The tweeter cone has foam damping around its periphery which may have perished.

The foam can be replaced so it's not a deal breaker, but it may be used as a bargaining chip.

 

[Galu]

This site gives the sensitivity of the Super 8 as a whopping 93dB!

Wharfedale Super 8 RS DD Fullrange Loudspeaker Measurements Data and Information Full Range

The author has measured the Theile/Small parameters which could be used to design a reflex enclosure of a size more suited to your purpose.

Fs: 69 Hz
Re: 9 Ω
Qms: 4.52
Qes: 0.80
Qts: 0.68
Vas: 21.3 ltr
Le: 0.34 mH

P.S. In his conclusion, the author suggests a 'TWQT' enclosure. This acronym stands for 'Tapered Quarter Wave Tube'.

HiFi Loudspeaker Design

 

[Galu]

The author has measured the Theile/Small parameters which could be used to design a reflex enclosure of a size more suited to your purpose.

I'm afraid that a smaller enclosure than the one recommended by Wharfedale seems unattainable according to this vented box calculator!

HiFi Loudspeaker Design