Antoria Record Player and amplifier

[crackle]

I came across this Antoria amplifier and Gramophone today, and took some photos.
Valves are EF86 x 2 and an EL84.
Can anyone help with information as to the model numbers.

Thanks
Mike

[sp10mk11]

That looks like a serious bit of kit, I hope it can pulled to working.
Gary

[Edward Huggins]

I would date ths as c.1958, maybe used for Dancing lessons in a Hall. The amp will have high sensitivity and would make an excellent 5 watt Guitar practice amp.

[crackle]

Thanks guys, that's filled in a bit more information.

Mike

[ms660]

Yes, 1958 ish, see 4th picture and read post:

http://bb.steelguitarforum.com/viewt...404&highlight=

Lawrence.

[crackle]

Great, thanks Lawrence.
Mike

[crackle]

I have got round to looking further into this amp and removed the chassis prior to testing and restoration.
The main smoothing can is a 50 + 50 + 50uf and is dated 1956. But it could have been a couple of years old when fitted. It seems to be reforming quite nicely.

The OP transformer and mains transformers both seem OK, and both the bass speaker and the treble have a decent reading on the speech coil.

The speaker baffle has some severe problems with de-lamination of the plywood.
When I unbolted the bass speaker I was presented with a little cascade of slivers of ply lamination where they had fallen out of the slots cut in the ply for the baffle.

Mike

[Edward Huggins]

Plenty of smoothing uF and note the rotating mains TX for hum minimisation as well.

[crackle]

The amp works very well, I changed all the hunts caps and one electrolytic.
I believe the amp circuit is very similar to the Mullard 3-3. There is no grid coupling capacitor, the grid is connected to the EF86 anode via a 1k resistor. I dont pretend to understand how this works but there is -7 volts on the grid1 of the EL84, ans also -7 volts on the anode of the EF86. How does that work, I think I will have to read up on the Mullard design.

The selenium bridge rectifier was only delivering about 100v, so I changed it for 4 IN4007 diodes.
What is the opinion on adding a series resistor in the feed from the rectifier to the first capacitor. Just to err on the cautious I have added a 220 ohm resistor for now.
The anode and screen voltages of the EL84 are both 250v so it cant be too far out with the 220 ohm resistor in series.

The original EL84 was a little cooked and sounded weak, but with a known good valve in place the audio output is pretty good on my workshop speaker.

The cabinet is going to need a fair bit of work to get it into shape, that's next.

Mike

[crackle]

Originally Posted by crackle

and also -7 volts on the anode of the EF86. How does that work, I think I will have to read up on the Mullard design.
Mike

As I was going to sleep last night thinking of this I realised what I was doing wrong. I was measuring the EF86 anode voltage with the negative test lead still on the EL84 cathode. The actual voltage on the EF86 anode is 21 volts. This is a very low figure and is 6 volts less than the 28v drop across the EL84 cathode resistor.

Hence the -7 v on the EL84 g1 with regard to its cathode.

Mike

[crackle]

Sorry about the maths.

[PJL]

It looks like the front panel unscrews so save all the slivers of ply and buy a large bottle of wood PVA and filler!

[crackle]

I forgot to mention, I removed the 220 ohm resistor in the HT feed, and I believe it made a slight improvement to the OP level with the extra 10 volts on the anode of the EL84.

Mike

[PJL]

Did you check the EF86 anode resistor? There are a whole bunch of those 50's carbon resistors that you can rely on to drift with time.

[crackle]

Yes the 1M resistor is is not the usual Erie type and it is measuring 1.06M so I left that alone.
I tested the amp with the original Celestion 44 speaker propped up on the bench, even out of the cabinet my ears started to hurt at just over 1 watt, its a damn sight louder than my little 4 inch 6 ohm bench speaker. At full chat the amp pushes out about 6v AC into the bench speaker, I am expecting that to drop to about 4v RMS into the 3 ohm Celestion, so a good 5 watts, allowing for it to be turned down to a decent level of distortion it should easily produce 3 very loud good quality valve watts, or if used as a guitar amp 5 watts.

After lots of struggling I finally managed to get the speaker baffle out of the cabinet. It seemed every time I removed a bit of cabinet which was stopping it from being twisted out of the cabinet, another piece got in the way.

Anyway the baffle is now on the bench being glued back together. I made a little jig to enable me to clamp 4 strips of ply at a time. The ply cheeks have a layer of heavy duty plastic sheet stapled to them to prevent them from becoming part of the baffle (I hope).
I watered the PVA a little to help it to run into the slots, a rather messy job, its surprising how sticky PVA becomes on your fingers after a while.


Mike

[crackle]

The glueing up of the baffle really went very well, I am pleased with the results, there are a few voids but I was not bothered about filling every tiny gap with the slivers of wood.

I have given it a light spray with black paint to even out the colour, prior to gluing back the original Tygan speaker cloth.
The original cloth has shrunk somewhat, it was flapping lots at one side when I got the amp. Hopefully I can get it to stretch sideways a little.

Mike

[crackle]

The cabinet is all back together again and the amp chassis refitted.
The cabinet has been cleaned and some of the tatty tears in the covering glued back down, it actually looks quite reasonable now.
Here are a couple of photos, there is a little red pilot light in the top tight corner behind the speaker cloth which is not on in the photos.

I have made a couple of movies and may upload one later as a demonstration. The problem with the movies is the camera's automatic volume control makes it seem the amp gets no louder when the volume is turned up, but one thing it does bring out is there is hardly any distortion when the volume is at about 2/3rds and the amp is actually quite deafening.
Mike

[unitaudio]

That has scrubbed up remarkably well! Good effort!

Regards,
Paul

[stevehertz]

Antoria produced (and still do) a range of replica guitars (Les Paul style etc) that were very popular in the 70s. So that Antoria amp would be very interesting to guitarists into their vintage gear. It's rare, I haven't ever heard of one before. Worth making a good job of the restoration, which by the look of those photos, you have done, excellent.

[Tractorfan]

Hi,
For an amplifier of that quality, I'm surprised it's single ended. I'd have expected a push-pull output.
Cheers, Pete.