[acresm22]

I have a pair of mono EL84 tube amps pulled from a Roberts reel-to-reel that I'd like to get up and running. Unfortunately, I'm not a DIYer when it comes to amps. Do any of you have experiencing refurbing these amps, or know of anyone who does? I'd be happy to pack them up and send them your way for an overhaul. I do have the schematics.

Thanks.

[Scott F.]

I've had a pair of those sitting on my workshop shelf for about a decade. I came to the conclusion after looking at them that it was way too much trouble to do anything with them. Besides the difficulty you will have hooking sources up to them (since you aren't a DIYer), the output transformers and the power supply are a weak point of these amps.

By the time you pay someone to rebuild them, you will have almost as much in invested in them as it is to buy a nice used (for instance) JoLida 102b, EL84 based at 25wpc that will sound considerably better.

just my $.02

[acresm22]

Thanks for the advice, Scott. I read that the good iron is what made these amps desireable, but that could be wrong...

[Brett Buck]

I have a pair of mono EL84 tube amps pulled from a Roberts reel-to-reel that I'd like to get up and running. Unfortunately, I'm not a DIYer when it comes to amps. Do any of you have experiencing refurbing these amps, or know of anyone who does? I'd be happy to pack them up and send them your way for an overhaul. I do have the schematics.

Thanks.

    I think, if you are not willing/able/interested in doing some design and fabrication work, you would be a lot better off just buying something. What you want to do can certainly be done but it will take some knowledge and experience to get it right. Bear in mind that even with a wimpy EL84, we are talking potentially fatal high voltages, and in this case, likely replacement of a bunch of components (like capacitors) that have gone over the hill over the years.

I am not trying to discourage you but I would be surprised if anyone knows  - now - exactly what to do to get it working, and if they have to get it, figure it out, design something, then fabricate something, it is likely to be quite expensive and the results may not be all that great. It amounts to taking a few of your parts and designing a new amplifier - it *can* be done, but at some point it is hard to see what the goal might be, with many good alternatives.

   If you want to learn to sling solder or want an EL-84 amp, you couldn't do a lot better starting  with the Dynakit parts ST-35 kit. Sounds great, sufficient power for most purposes, EL84, and *dead easy* as a first kit.   If you don't want to tackle it (and you *can* do it - if you are able to function in society you have sufficient capability to learn to solder this baby together) I would be happy to assemble it for you for a minimal fee (contact me off-line if so). But I am sure you could do it yourself.

    If you just want a tube amp, the best I have ever heard is the AVA Ultimate 70 or the very similar item in a better chassis, the Ultravalve 70. The Ultimate 70 is FAR AND AWAY the best tube amp I have ever heard and that's quite a lot of them over the past 50 years. And for something that could arguably be the best tube amp you can currently get, it's very reasonably priced. It's certainly much better than any McIntosh, CJ, or VTL that I have heard, not even close, really and a tiny fraction of the cost.

    There are some less-expensive tube amps from various sources in Asia, and they are generally pretty tolerable to listen to, if not in the highest echelons of hi-fi.

     Brett

     

[planet10]

These can be used to make a nice pair of RH84-style monobloks

http://www.diyaudio.com/forums/tubes-valves/158330-akai-m8-rebuild-restore-will-work.html

You do need to strip out most of the parts & rewire them and install new parts.

If you aren't going to diy them, the cost to pay someone to do it would usually be better spent on a new amp... something like the new EL84 miniwatt.

Pass them on to someone who'll diy them, if you don't.

dave

[doug s.]

I have a pair of mono EL84 tube amps pulled from a Roberts reel-to-reel that I'd like to get up and running. Unfortunately, I'm not a DIYer when it comes to amps. Do any of you have experiencing refurbing these amps, or know of anyone who does? I'd be happy to pack them up and send them your way for an overhaul. I do have the schematics.

Thanks.

these are fantastic little ~5wpc el84-based set amps, competitive w/the spendier alternatives, imo.  i have a pair, pulled from the m8 tape dack, that is fed from that deck's original power supply.  (getting the schematics helped me determine the proper way to plug the amps into the power supply harness.)  i beg to differ w/scott f. here - power supply and output transformers are killer, for a 5wpc set amp, and build quality is superb.  if your amps are in good shape, you will get excellent sound, w/no mods at all required.  all that is needed are 1/4" fono plug adapters, both for the rca's and for the speakers.

you can contact donn tarris for more info if you wanna go nuts on them - some people do, but mostly pros who turn them into killer mic preamps.  i emailed donn for tips about the best way to hook up the inputs/outputs for use as audio amps, and he told me mods aren't really necessary - unless, of course, you want to get extreme.  build-quality as-is, is excellent...

http://www.vintageaudio.org/home.html


q&a i had w/donn:

> hi,
>
> i saw your website for the roberts tape deck amps, &
> was a bit interested in what you do w/these amps. 
> i have a mint pair of akai m8 amps that i am
> presently using in an audio system.  i have figured
> out how to power them up from the m8's original power
> transformer.  i take inputs from my preamp into the
> inputs at the top left of each amp, & i have wired a
> 1/4" fone plug to normal speaker binding posts for the
> speaker outputs.  they sound really nice into
> 97db-efficient 14 ohm speakers.  the gain on them is a
> *ton*, i have to barely open the wolume pots to get a
> lot of gain.  the tone is fully max’d out to get flat
> frequency response for a normal stereo rig.
>
> what i am wondering, is what, if anything, can be done
> to mod these for better performance as normal stereo
> amps.  when i got them, they looked like they had
> never been used – really amazing.  i am not interested
> in using them as preamps, tho i may be interested in
> retaining their volume pots...
>
> thanks,
>
> doug s.

Hi Doug,
By default, the top switch on the units is spring loaded to
the playback position, which is accessed on the top left input.
This goes to the EF86 input tube, which is set up for a "ton"
of gain, to amplify the signal from the tape deck head. The eq
is also set for playback based on their output response curve,
which means you need to have the tone control full on.  It
would work better to remove the top bar and spring assembly to
allow the switch on the top to be set to the record position,
which would then have you plugging into the input second from
the bottom on the left, the line input. You could also go into the
lower left input, normally for a high impedance microphone, giving
you more gain. Your frequency response should be better through
this circuit.

The speaker output on these is normally 8 ohms, so your amp is
working a bit hard to deliver to 14 ohm speakers, but should be ok.

Let me know if this helps.
Cheers,
Donn
----------------------------------------------------
doug sedon wrote:

> thanks, this makes sense.  i was wondering why the
> line input dint work - i have to set the spring loaded
> switch to record, eh?  i noticed this switch disables
> the amps when i manually move it, & the feed is going
> into the top left input.  :>)
>
> so, disabling the "playback" switch & setting it to
> "record", & then using one of the other two inputs
> will give me better sound?  how will it affect the
> tone control?  it *does* sound flat w/the tone max'd
> out as i am now using it.

(donn):
tone isn't in the record circuit, it plays no part, just flat... In
theory, you shouldn't need the tone control in the playback.

doug sedon wrote:
> i surmised the amp was 8 ohms, & i wasn't getting the
> power out of it i should be, w/14 ohm speakers - do
> the output transformers have a 16 ohm tap?  do you
> know what the power rating of the amps are?

(donn):
I think the amps are about 8 watts, not sure if there's a tap for 16
ohm, I don't believe so.

doug sedon wrote:
> also, what (if any) mods/upgrades would you recommend
> for using as power amps - i know your site seems
> dedicated to using these as preamps...

(donn):I don't think you'd need much more. You could replace the power caps,
etc, clean all the contacts, pots...
--------------------------------------

ymmv,

doug s.

[planet10]

Thanx doug, that was very helpful. I have 6 of these (2 will remain in the tape deck)

dave

[acresm22]

Yeah, thanks Doug...great info.

I'm going to dust off the Roberts monos this weekend, spray some contact cleaner here and there and see if I can get them singing (using those hookup tips from vintageaudio).

Dan

[doug s.]

dan/dave, let me know what y'all think. i think they are definitely worth the effort to get running.  comparable, imo, w/my almarro a205a mkll, that has upgraded tubes and caps...

doug s.