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ThSpeakerDude88 16th April 2008 03:01 AM

RH84 vs Magnavox SE?
Any opinions? I have two of the neat old Magnavox 86 chassis. One is restored with the feedback loop modified, the other has been gutted for restoration and I want to try the RH84 circuit in this one, if its worth it.

I'm gong to be creating a webpage as I go along for other DIY'ers to see how to restore/restomod these old amps as a budget Hi-fi system.

I'm also open to CCS on the input or output stages, as well as possibly negative bias ( havent heard of it really in SE amps???)
I want to keep pentode mode to keep the measly high power (triode connected doesn't give enough power at all for most normal efficiency speakers), so lets try and make a SE pentode amp sound as good as it can here.

planet10 16th April 2008 03:34 AM

One of my RH84s has Magnavox OPTs...


ThSpeakerDude88 16th April 2008 04:10 AM

How does it do on bass? smallish size obviously limits bandwidth...:dead: Wonderful high end though.

planet10 16th April 2008 04:21 AM

The speakeers i use with it go to 70 Hz... it seems fine.


ThSpeakerDude88 16th April 2008 01:32 PM

Any huge differences in sound or responce between the two?

planet10 16th April 2008 06:11 PM


Originally posted by ThSpeakerDude88
Any huge differences in sound or responce between the two?
The one with the maggie OPTs represents available choke & OPTs installed in the last of the single chassis development (we worked thru about a dozen variations and it was probably a bit over half-way). The monoblocs have twice the powersupply, an EF86 instead of 12AT7 in the front, are parafeed (with a roll-off of about 50 Hz), and use better Grundig OPTs. They are definitely better (they took on some Audio Note Conquerers and it came out a draw (with a caveat -- the earlier roll-off complimented the room/speakers better)).


ThSpeakerDude88 18th April 2008 05:15 AM

Are you sugguesting the magnavox transformers as parafeed chokes? :xeye:

BTW, I am planning on wiring up this amp this week, but have experienced a major setback :(

while cleaning the power transformer and prepping it for paint... I dropped it and caught it by the wires-several pulled out of the end bell. Darn it! No getting these transformers apart either, their heavily potted and you CAN NOT get the screws out of the transformer!! Don't even try! I've had this happen before and they snapped off and I ended up drillng them out- which was a pain in the butt! I just tossed the tranny. Sad.

Know of any suitable replacements? The original voltages were 225-0-225 , 6.3v, 6.3v. The radio was rated at 90 watts , but I won't be drawing that much from it with just the amp.

How much current do I really need on the HT side with two SE 6bq5's and one preamp tube?

planet10 18th April 2008 08:20 AM


Originally posted by ThSpeakerDude88
Are you sugguesting the magnavox transformers as parafeed chokes?
No... but the primaries from a set of OPTs can be used as parafeed chokes (we use a 2nd Grundig in ours -- ie 1 console per channel was primamry iron donor)


ThSpeakerDude88 18th April 2008 01:53 PM

Thats kind of what I meant, but being so small and not having much inductance already, the magnavox OPT's probably would not make good PFC's would they? I do have four of them if it would,however, how does this affect the plate load, wouldn't it be halved since you're essentially paralelling them, or does the DC cap between the plate load and the OPT eliminate this resistance mismatch?

planet10 18th April 2008 03:48 PM

You aren't paralleling them. The small inductance will effect the bass roll-off thou. The Grundigs we used are about 13 H and with the 3.3 uF cap the bass starts rolling off in the 50 Hz neighborhood.


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