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Old 9th February 2012, 03:30 PM   #1
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Default newer than noob looking for advice on RH84

Hello I am new to DIY Audio. And I am looking for some advice and assistance.
I have very little electronics experience but I am attempting to learn. I want to get into Tube Audio but have no real budget to speak of. I acquired a Zenith 5k29 AMP pulled from a Console and thought I might be able to rework it. However with my lack of electronics knowledge I was quickly overwhelmed by the complex circuit. I should probably build a simple kit where all of the parts are included(or at least there is a clear parts list specd out) and all I need to do is stuff a PCB and then wire it up in a Chassis. I am very intrigued by the Decware kit.
Zen Triode SET kit amplifier model ZKIT1
But I keep looking at the Iron on this Zenith and thinking maybe I can reuse it. It has been suggested that I should be able to use the iron from Zenith in an RH84 build. From what I can tell the RH84 is a fairly simple design that many use as their first time foray into tubes.

I have looked at the schematic but what is simple for most is like a new language to me.

So I am looking for some confirmation Can I use this iron on an RH84, does there need to be any modification the components to in circuit accommodate my transformers or can I just build it per the schematic? Has anyone actual created a Parts list or BOM that they can share?

Am I kidding myself, should I just bag it and wait until I have the money to buy a Kit?
Anyone willing to mentor me?

I just purchased a set of Audio Nirvana Standard Eight Full Range and I am building their 1.3 eclonsures. My play is to build an Oatley K301 RIAA Pre or some other simple Phono pre. I Just want to listen to my Vinyl through some Tubes
Thanks
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Old 9th February 2012, 04:25 PM   #2
GloBug is offline GloBug  Canada
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Normally I'm all for reusing stuff, but in this case I would go for the Decware kit.

I'm sure the Zenith could be used for something, keep it around. I just did some quick searching and I can't find the specs yet for the Zenith transformers. They are out there and it is "doable", it just requires more research and time. You would basically be rebuilding it so the current complexity could be ignored.

If you have cash = Decware
If you have Time = Rebuilt the Zenith.

Lot's of folks here to help.

The first thing to do with the Zenith is find some specs for the Output Transformers to be sure they are suitable for an RH84. You want to find out the "primary" and "secondary" impedance.

If you can't find the specs, it is possible to measure yourself, but it is much easier in this case for you to google.
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Old 9th February 2012, 05:12 PM   #3
TheGimp is offline TheGimp  United States
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I have located the schematic for the 5K29 amplifier chassis. If it is the one you have it has 5 tubes, 5Y3GT rectifier, 12AX7 first amp stage, 12AU7 driver stage, two ea 6BQ5 output tubes.

The speaker compliment was four per channel, 12" bass, 5" mid, two 3-1/2" Tweeters.

No impedance info is given, but I believe most console speakers were nominally 16 Ohm for amps of that era.
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Old 9th February 2012, 06:25 PM   #4
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Default does this help

I have the sams photofact for the console but it was too large to post so I made a screen shot of the transformers and speakers section
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Old 9th February 2012, 06:51 PM   #5
GloBug is offline GloBug  Canada
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OK, so the RH84 uses a 5,000ohm output transformers.

The Zenith has according to the Photofact, 9,600ohm output transformers.

So as is, it would not work out great directly connected to 8ohm speakers.

Not all is lost if you have more speakers. See, the amp does not see the speakers you have connected, if you use speakers with less impedance, the amp will see less impedance reflected back to it through the transformer.

Somebody with the numbers could chime in with an exact figure, but basically you parallel speakers together to effectively make a lower impedance speaker.
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Old 9th February 2012, 07:31 PM   #6
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Can someone post the schema. The Grundig OPTs we used for our RH84 were closer to 9.6 than to 5k -- close to what the Decware OPTs are. Just means lower distortion and a bit less power.

In Canada Zenith OPTs were usually made by Hammond, in the US likely different.

Fatuncle, can you post some pictures?

dave
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Old 9th February 2012, 07:45 PM   #7
TheGimp is offline TheGimp  United States
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Those item numbers don't match the schematic I have. I show outputs as T1 and T2.
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Old 9th February 2012, 07:52 PM   #8
chrisb is offline chrisb  Canada
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Quote:
Originally Posted by GloBug View Post
Normally I'm all for reusing stuff, but in this case I would go for the Decware kit.

I'm sure the Zenith could be used for something, keep it around. I just did some quick searching and I can't find the specs yet for the Zenith transformers. They are out there and it is "doable", it just requires more research and time. You would basically be rebuilding it so the current complexity could be ignored.

If you have cash = Decware
If you have Time = Rebuilt the Zenith.

Lot's of folks here to help.

The first thing to do with the Zenith is find some specs for the Output Transformers to be sure they are suitable for an RH84. You want to find out the "primary" and "secondary" impedance.

If you can't find the specs, it is possible to measure yourself, but it is much easier in this case for you to google.


Check with Decware - sections of their site need updating, as I think they're no longer selling complete kits, particularly including the proprietary OPTs; the $45 gets you a PCB and parts list (recommended OPTs= Edcore). The latter and schematics are readily available on the website, so if you're at all inclined and have a decent parts bin, you could save the price of the kit and just build from scratch. Handwired PtP was always part of Steve's mantra, and for well over 10yrs the original Zen A through C kits were exactly that.

I just listened to one again for the first time in a few years last night - a sweet sounding little amp, a close approximation of which could easily be DIYed for probably $400, depending on how silly you wanted to get with tube set and boutique coupling caps, etc. With a well stocked parts bin or organ donor chassis, probably less than half that amount.


edit: actually reading the Decware site more thoroughly, I see an estimate for the complete kit using the recommended Edcore Iron as approx $220, less taxes, tubes and chassis etc.
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Last edited by chrisb; 9th February 2012 at 08:06 PM.
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Old 9th February 2012, 07:57 PM   #9
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Thanx gimp, in the meantime i actually found a more complete schema (since it is cleaner & smaller i replaced yours -- hope you are OK with that)... and a pic.

This amp is VERY similar to the one that, with RS 40-1197, got me going in my current frugal-phile(tm) direction.

THis is exactly the kind of donor amp that thr RH84 was targeted at. Strip the chassic down to the iron, replace the tube sockets (3 x 9 pin + 1 for the rectifier), add a choke (Hammond makes a 10H 100mA that is perfectly suited and cheap), RCA's in and binding posts (ApexJr is a good source) and go to town.

The thing that made the biggest differenc eon our builds was use of Solen poly caps in the power supply.

dave
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Old 9th February 2012, 08:02 PM   #10
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Quote:
Originally Posted by chrisb View Post
I just listened to one again for the first time in a few years last night - a sweet sounding little amp, a close approximation of which could easily be DIYed for probably $400, depending on how silly you wanted to get with tube set and boutique coupling caps, etc. With a well stocked parts bin or organ donor chassis, probably less than half that amount.
With a donor like yours, if all the tubes are good, you could probably put an RH84 (or a Decware clone, what we started with, ending up with RH84) for <$100=150 (including Solens (2x32 @ 400V would do))

dave
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