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JKent

Advent 400 table radio

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Hold on: This should help

 

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There are 15 electrolytics (including the NPE in the speaker). They are gray jacketed and some are marked Unicon. They're 40 years old, so this time I replaced the ones on the amp board and the tuner board. Here is a list of the caps, along with the measurements of the ones I just pulled. When I replaced, I went up one step in voltage ratings (replaced 16v with 25v, 25v with 35v etc) and used 105 degree caps if I had them on hand. Replaced the speaker cap with a PIO. Those guys sure liked hot melt glue!

  • 1000uF 35v radial (measured 1081)
  • 220uF 35v radial (measured 290)
  • (3) 100uF 25v radial (measured 133, 135 & 139)
  • 47uF 16v radial (measured 66.4)
  • 10uF 25v radial (measured 13.13)
  • 10uF 16v (measured 14.46)
  • (4) 10uF 16v axial (measured from 14 to 18)
  • 2.2uF radial (measured 3.56)
  • 1uF 50v radial (measured 1.47)
  • 1uF 50v axial NPE speaker cap (tossed before measuring)

 

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Check out this thread: http://www.classicspeakerpages.net/IP.Board/index.php?/topic/8443-advent-400-table-radio/

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13 minutes ago, JKent said:

Welcome John

Here's a schematic.

-Kent

oops. Just noticed it doesn't give the values. I'll keep looking

Advent_400_radio_schematic_only.pdf

Thanks for the fast response!  I 'm going to digest this.  I'm learning a lot about electronics and this project is way cool.  I'm thinking of upgrading the voltage of the caps I replace to something just above what I take out.  Anyone have experience soldering modern lead free solder onto the existing solder?  

 

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Going up a step in voltage is probably a good idea.

I would not use lead-free solder.

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Hello, and thank you, this thread has been informative.  I have an Advent 400 and a couple speakers, as well as the original manual.  The list of caps will be handy, I'll be doing mine eventually.  Fortunately my radio works very well and has a nice faceplate, but unfortunately the person who shipped it to me faced the knobs of the tuner toward the somewhat delicate grille of the speaker and dinged it up a bit, it was mint.  All have yellowed cabinets, but I've managed to fix that without a lot of elbow grease-more on that in a sec.

First, a question:  In the instruction manual for the radio, mention is made of hooking a second 400 speaker up, but no information is given as to how to do this, it says those instructions are available with the purchase of an accessory speaker.   Does anyone know how?  It would be handy to have two speakers running.  

As for whitening the cabinets, I've used creme developer from the hairdresser shop and several hours of bright sunlight, the yellow fades nicely.  I have only done one speaker (too busy enjoying the radio to pull it apart yet) and I'd say it's 80% back to white, the interior of the cabinet makes for an easy comparison.  I will try and get some pics tomorrow.  It's sort of hard to believe how well it works.  I read somewhere that people add a little oxyclean as a catalyst, might try that also. 

If nobody has done so already I'd be happy to scan/upload the manual for the radio.  It's informative and very much in the Kloss/KLH style.  

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Welcome Shogun

12 hours ago, shogun700 said:

In the instruction manual for the radio, mention is made of hooking a second 400 speaker up, but no information is given as to how to do this, it says those instructions are available with the purchase of an accessory speaker.

hmmmmm. The manual I have doesn't even say that much. It just says "An additional Model 400 speaker system is available as an accessory for use in the same or another room." It also says the speaker is 8 ohms. My guess would be that the wires for the 2nd speaker would be hooked up to the same terminals as the main speaker but it does not say that the amp is rated for 4 ohms.

My GUESS is it's OK. The original KLH Model Eight had an extension speaker that just piggybacked on the connector for the main speaker (but that was a tube radio). The KLH Model Twenty-One (transistor) had both an "Extra Speaker" jack and a "Remote Speaker Alone" jack, so its amp COULD drive two 8 ohm loads simultaneously. So my guess is that given Kloss's history of putting two 8-ohm speakers on a single output and the fact that there is no other apparent way to hook up the 2nd speaker, wiring it in parallel may be OK.

But I'm not an electronics expert. Maybe a member with more knowledge will have a better answer. It's possible the instructions that came with the accessory speaker showed hooking the speakers up in series.

Kent

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Kent, thanks for your response.  Your logic makes sense, you'd just think if it was as simple as hooking it up through the same jacks they would have just said so right in the instructions!  Either they wanted to avoid people hooking up random speakers, or they really did need to be connected in series.  I'm sure we will figure it out in due time, for now I'll just use one speaker.

   

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These little radios are quite forgiving. Back in the '80s, I used one of my Advent 400s with a large PA cabinet that had one very efficient 15" JBL driver at 8 ohms and a high frequency horn that was filtered for HF - got many hours of loud music out of this thing without any issues. I'm certain that connecting a second Advent 400 speaker, either in parallel or series, would not affect the radio adversely.  

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Nice tidbit of info bhart-I'll fearlessly hook up both speakers-once I get it all back together.

Here's a photo of the unrestored radio next to a whitened-with-hairdresser-peroxide speaker cabinet.  I'd say it's 90% white/back to original.

 

 

20190728_085314.jpg

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10 hours ago, shogun700 said:

Here's a photo of the unrestored radio next to a whitened-with-hairdresser-peroxide speaker cabinet.

Wow! Nice job! I thought it was impossible to whiten those.

I did a little googling and found "40 Volume Creme Developer" for about $4. Is that the stuff? You mentioned elbow grease, so what did you do?

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I've had similar success with salon peroxide.  I painted it on as thick as I could and then wrapped it in clear plastic wrap and left it in the sun for a couple of days.  Looks like new.  

I'm now replacing capacitors and probably the two transistors under the heat sink.  The circuit board under the transistors looks burnt.  A friend said I should look upstream from the transistors too.  (I'm in over my head with the electronics.  We have "Fix-it-Friday" at the Maker Works where I have my office - lots of help)

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11 hours ago, JKent said:

Wow! Nice job! I thought it was impossible to whiten those.

I did a little googling and found "40 Volume Creme Developer" for about $4. Is that the stuff? You mentioned elbow grease, so what did you do?

No elbow grease, jsbarrie has the right idea.  I used a big ziploc bag but I think I like his plastic wrap idea better, the ziploc is a little translucent and there's the label on one side that shades things a bit.  40 Volume Creme Developer is the stuff, can't remember what brand I have.  It works great on KLH knobs also but keep it off the brown center insert, it will bleach that right out.  Oops...

1 hour ago, jsbarrie said:

I've had similar success with salon peroxide.  I painted it on as thick as I could and then wrapped it in clear plastic wrap and left it in the sun for a couple of days.  Looks like new.  

I'm now replacing capacitors and probably the two transistors under the heat sink.  The circuit board under the transistors looks burnt.  A friend said I should look upstream from the transistors too.  (I'm in over my head with the electronics.  We have "Fix-it-Friday" at the Maker Works where I have my office - lots of help)

Great tip about putting it on thick, and I didn't realize you could leave it on that long.  Will try that next time.  

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Kent and others,

I'm very pleased to find all the information on this link.  I have a 400 in very good cosmetic condition, except for the yellowing, and I'd like to give it a tune up.  I know very little about electronics but do fairly well with soldering so hope I can join those who have been successful.  I suspected at the very least the electrolytics should be replaced.  In particular the cabinet restoration should be useful.  I'd planned to paint mine.  :^(

I also had a KLH Model 8 that I hoped to restore but never found the time.  A friend who is a speaker manufacturer put me in touch with someone associated with the new KLH and we worked out an agreement of sale.  Some may be disappointed to hear that but I sold the KLH for more than the Advent is worth and I could only use one.

It may be a few months but I'll report back on how successful I am.  Thanks again.

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Hi All,

I have an Advent 400 that is in working condition and I am using it with two of the advent 400 speakers. It sounds great so maybe someone has already done the refurbishment.

I am wondering if anyone has used Auxiliary cables with this model to hook up an iphone or other music/radio/podcast source? current or more commonly purchased cables do not seem to work/are too small. 

Does anyone know of an adapter to purchase for this, or a cable that can be purchased and used for this purpose?

Much appreciated for your support and insight. And, maybe I am the only one, but I kind of like the funny yellowed color :).

Mindy

 

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Hey Mindy. Welcome.

It can be done but not easily. There is a Mono input on the back of the radio. You need a stereo-to-mono summing box as explained in this article: https://www.prosoundweb.com/why-not-wye/

I make a gadget like that to feed a stereo input to the KLH Model Eight but it won't work with the Advent. If you have some soldering skill you can make your own, or send me a PM and I'll work up a price to build one for you. 

Kent

 

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OK. Just for giggles I cobbled one together. Photo shows an iPod with 1/8" headphone jack. Also tested it with an iPhone 11, with Lightning-to-1/8" adapter and that also works.

 

 

 

 

 

stereo2mono gadget 10.jpg

stereo2mono gadget 7.jpg

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Here's another twist on my Advent 400 mods.

One of my speakers was dead. Kaput. So I looked for a drop-in replacement. Found a guy on ebay selling a pair of Wharfedale 5.5" mids for a reasonable price and they fit the bolt pattern. They turned out to be nice drivers but a little dull for the radio. Probably really mid-woofers and not truly full-range.

I happened to have one orphan "Apex Jr." tweeter left over from another project. They are no longer available but at a buck apiece I'd ordered a spare. Had to mount it behind the plastic baffle otherwise it would not clear the metal grille. I used a file to chamfer the edge of the plastic, sort of like a very thin wave guide.

I considered running the mid/woofer full out and just adding a capacitor to the tweeter but Roy suggested a coil on the woofer. Sorted through the parts box and didn't find anything that seemed right so I got a generic 2-way crossover from PE. There were some nicer ones at a lower price on ebay but I didn't want to wait for shipping from China.

The PE xo worked well. I did add a small paper-in-oil bypass cap just for fun. Have not done much A/B comparison with an original speaker because my Advent 400 radios are in the shop but I think this was successful.

Kent

Advent 400 2-way mod 1.jpg

Advent 400 mod_2.jpg

Advent 400 mod_4.jpg

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Hi Kent,

I appreciate your follow up.  After moving 2/3rds of the way across country last summer and some health issues this year I'm way behind on several projects.  One of those being the Advent restoration.  ButI want to complete that so I can use it in the kitchen while fixing meals.

When I saw your photos I was going to ask about the black paint you apparently used on yours.  That looks good.  But then re-reading a couple of previous posts on applying peroxide suggests I should try that first.  If not successful then the black paint would be my next choice.  Either color will match where I'll place it.

Now to get going on things! ;^)

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It takes more than just peroxide. It's a process called "retrobrighting". Google it and you'll find info. I used "40 Volume Creme Developer" and OxyClean, put it in a clear plastic bag out in the sun for days. The plastic got pretty white. I've read that the laundry brightener to use is TAED. Dunno whether that's in Oxy. Also don't know if there is a better product than the 40 Volume Creme Developer. But do a search.

The black pebble finish is PlastiKote Truck Bed Liner https://www.amazon.com/gp/product/B0041DK44O/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

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One more thought on these. The metal grille is held in by a rubber spline that tends to dry out and break if removed. A good replacement is window screen spline. It took some trial and error" .125 diameter is too thin, .175 is too thick. But .150 is just right

https://www.amazon.com/gp/product/B00LFQL8WM/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&psc=1

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Thanks Kent, a great tip.

I'm dealing with a couple of health issues but hope to soon pull out my 400 and at least do the bleaching with the two cabinets while summer is here.  The electronics may wait a little longer.

I'll post results eventually.

BTW, love your Gromit image!

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