Radford System

[florin]

That's a nice enough combination of drive units.

The HF1300 tweeter cuts off rapidly above 13kHz and a Coles supertweeter can be added on a separate filter without modifying the existing crossover.

If you are over the age of 45, aiming to extend the frequency range up to or beyond 20kHz is likely to be of limited value.

I doubt you'd gain any benefit from changing the B139.

The capacitors are probably in need of replacement, there are so many choices it would be best to look for what meets your needs.

The rear connection terminals are horrible and could be usefully upgraded.

If it was me, I'd just change the caps and terminals in order to retain a fair degree of originality on what is a collectible speaker.

I have tested the Coles 4001G on their own on both the B&W DM2 and DM4 and I can well hear them going. I'm 40 so I don't expect to loose my hearing in 5 years time, at least I hope so lol.

I gave up on the idea of having a SP1044 to replace the 6171 version of the KEF B130 which is larger and it would have made more complicated.

Regarding the input terminals I was thinking to replace them however I don't want to get banana jacks as this would imply too much hassle and would have to do a cut-out to mount the plastic box at the back which is just too much work.
I could also just stick banana jack terminals in the existing holes that I don't want to have them stick out so my thought is to buy copper bolts, screws and washers and keep the back flush maintaining the same design and as you say its originality.
I did some math on the economics of it and 4 pairs of copper screw with washers and nuts would cost me £20 however they only come in packs of 10 each from China. I was thinking I could order 10 or 20 and sell the other pairs back on eBay.

Now coming back to mounting the Coles I had a second look at the crossover and noticed in a corner HF2+ / HF-.
Turns out the Radford "Monitor" model shares the same crossover with the bigger brother model "Studio" which employs a Telephones Supertweeter 16ohm.
By the looks of it the only missing pieces I need to add to the existing crossover are a 0,47μF capacitor and an inductor to which I don't know the value. Any idea what μH inductor I would need? The DM4 crossover uses a 0.200mH before the Coles 4001G whereas the DM2 uses 0.3mH

In regards to positioning, my plan is to remove the mids driver, patch the hole and then reposition it further to the side so I can fit the Coles in the middle. They will be quite close packed.

I've made a side by side comparison of the two Radford FN7/5 showing them side by side.Untitled copy.jpgUntitled copy_2.jpg

[Lawrence001]

Can you not fit the Coles above the HF1300 would be a lot less hassle and they wouldn't sound any different.

[florin]

Can you not fit the Coles above the HF1300 would be a lot less hassle and they wouldn't sound any different.

It would be much easier wouldn't it?
I would need to build new speaker grills or drill a hole on top. Also they are not mirror image of each other like the B&W DM2's are.

[walpurgis]

I have tested the Coles 4001G on their own on both the B&W DM2 and DM4 and I can well hear them going.

That tells you little unless you know the frequency the Coles is introduced at and the filter slope.


There are many tweeters that could be used, you don't have to stick with the Coles. Anything with a smoothish response above 13kHz could be considered.

I'd mount the supertweeter in a separate module/baffle above the main speakers. And I'd use a separate filter with it.

[Lawrence001]

That tells you little unless you know the frequency the Coles is introduced at and the filter slope.


There are many tweeters that could be used, you don't have to stick with the Coles. Anything with a smoothish response above 13kHz could be considered.

I'd mount the supertweeter in a separate module/baffle above the main speakers. And I'd use a separate filter with it.

It's more period authentic though. Most of the 60s/70s designs that used the Celestion/Coles combo had switched to a single more modern tweeter by the late 70s as they were much improved in output and frequency range.

If you're looking to fit a more modern tweeter you could drop the HF1300 and just fit a new one there, adjusting the crossover of course.

[florin]

I was thinking of that however it would still have to be 16 ohm?

I'm not very proficient with crossover design so operating modifications on the existing crossover would need doing some research and I don't have instruments to verify filter slopes etc.

I have a pair of Acoustic Research AR18LS tweeters that are 8ohm and can reach 20kHz on their won but obviously don't know what the implications of replacing the 16 ohm Celestion with the 8ohm AR would entail in terms of crossover modifications.

The only 16ohm tweeter replacement I've found is the Beyma CP22 https://www.ebay.co.uk/itm/133904639...0AAOSwZAthaXrW
Don't know if this would be a good match though.

[walpurgis]

I was thinking of that however it would still have to be 16 ohm?

It doesn't have to be 16 ohm. At higher frequencies, you are dealing with smaller wattages and impedance is relatively less crucial.

There are many interesting tweeters on the second hand market. I favour old non-ferrofluid types myself. The KEF T27 works really well as a supertweeter.

[florin]

It doesn't have to be 16 ohm. At higher frequencies, you are dealing with smaller wattages and impedance is relatively less crucial.

There are many interesting tweeters on the second hand market. I favour old non-ferrofluid types myself. The KEF T27 works really well as a supertweeter.

My answer was to Lawrence "If you're looking to fit a more modern tweeter you could drop the HF1300 and just fit a new one there, adjusting the

crossover of course." in the idea to drop the HF1300 and replace it with a tweeter that covers the whole top range of the spectrum. The Acoustic

Research AR18LS is a 50w two way acoustic suspension 48Hz to 25kHz crossed at 2000Hz and the tweeter is paper cone however it's 8 ohm so it

wouldn't be a replacement like for like since the HF1300 is 16ohm.

[Lawrence001]

There may be workarounds like adding a resistor in series. The relative sensitivity is also important. Someone more knowledgeable than me could say more.