Have a chassis out of a Rymola 254-81 which I beleive may have been used in other brands as well? Info for this brand is very scarce. In fact any info at all is welcomed greatly!!
Chassis works OK & pulled in stations well & sounded excellent. valves etc are OK but I have no idea on what O/P transformer to use on this chassis. Tried a 10k primary using a Jaycar PA system transformer which has selectable impedances from 20k-2k ohm but the 6V6GT audio output tube got VERY VERY hot VERY quickly suggesting I guessed incorrectly.???
Only picked 10k because thats what my healing uses which also uses the 6V6GT as the audio O/P.
Anyway the 6V6GT tests OK- 86% no grid leakage & no shorts. All surrounding components appear OK & in very good condtion despite their age.
Is it possible the 6V6GT would get hot that fast from to high an impedance on the O/P transformer or should it just glow "red" as per O/CCT ?
Should I try 2.5k ? Don't want to damage or stress anything again if possible but I do not posses enough valve knowledge nor information to calculate what it should be.
Any help suggestions welcome or a CCT diagram would be great!!

Hope this allowed on this forum but here is the link to view a pic of what this radio would have have looked like before the chassis was removed.............

http://thebakeliteradio.com/page81/page81.html
Anyway thanks in advance to anyone who has the info & time to respond

Circuit does not mention value. If you have the original it may be on it?
What was wrong there. Its DC resistance will not be 5 - 7 K

At 250V HT 5000 Ohm primary to 7000 is normal.

The tube nominally runs with around 45mA Plate current at that Voltage (Zero signal). Valves normally run hot. Rectifiers & Output tubes, the hottest. If the plates glow red, thats the time to panic.

The 100V line transformer is not designed to handle DC. There are universal Audio transformers about.

Marc

G'day Marc & thanks for the Response
Unsure of original values, all I have is the radio chassis & dial face on two bits of timber minus speaker etc. It was found in a garage clean up by a friends inlaws & I was attracted to the "glowing technology" hoping to learn & turn it into some sort of functional unit & worry about a cabinet for it after it was all working OK.

Have no idea what the plate currents are, have a friend who has performed that on his Marshall PA amp so will get advice on that one first if its a neccesary.

I didn't notice if the 6V6 was glowing red as I could "smell" it was hot -paint smell starting to blister! & turned it off straight away & now I am reluctant to turn it on again.....took some time to find a good 6V6GT for a reasonable price. Have been going to Amatuer radio Hamfests etc for parts so far but only found one.

I am hearing you about the transformer so will try & locate a suitable unit.
When you say universal I assume that means various tappings (Z) to choose from? So I will hunt about unless you can post a link.

Would too hign an Impedannce on the transformer cause the heat issue though??

Thanks Again

It would appear that something is very wrong in the wiring of the 6V6 and one needs to get a copy of a 6v6 circuit or that radio's and become au fait with it and the basics of how it all works.

This could also extend to the Power supply as having been hacked about, one does not know what has been done to it ?

Transformer will only have 7K of inductance when it has an AC signal through it. Transformers & Inductors may well be close to a DC short, when measured with an Ohm meter.

A classic non radio comparision is the Kettering Ignition used on cars prior to electronics. They would draw near 3 DC Amps with the engine stopped (ignition on) and a bit less than two running.

DC Resistance & Inductance are two very different animals.

The plate current will be reduced three ways; viz.:--
By increasing the resistance in the Plate circuit.
Reducing the voltage on it.
Normally the current is controlled by the grid, the controlling voltage of which is set by the Cathode resistor.

In this set, it is back biased, and that resistor sets the bias. -12.5V with 250V HT

6V6 is a Pentode which means that it also should have HT voltage on its screen (Pin 4). Commonly HT is connected to pin 4 along with one primary wire of the transformer and the other goes to the plate pin 3.

It may be an idea to send Brad a pic of the inside of the pan for posting as this is going to grind to a bit of a halt without more info.

Marc

Thanks Marc, will try find Brads email on here some where, in the meantime I will also draw out the CCT diagram as it stands now to accompany the PIC. No mods appear to have been made to the unit -other than removal from its original console! (shame) ;(

Will attempt to get this done by this Friday, work & family always get in the way of these projects!!
Thank God & Brad for this website!!!
Paul

I have forwarded a copy of a circuit, to which I have added pin numbers, to Brad and asked him to send it to you.

Reverse engineer that, & see if it is what you have; That may save a lot of grief & time.

Marc

Bradmail.vintage-radio.com.au

Tar, look forward to receiving it, have sent pics of unit to Brad to forward/post.


Many Thanks.

They've arrived safely. I'll post them tomorrow morning.

OK ..... Brad has kindly forwarded the pictures to me and others will look forward to seeing where I am about to go.

Looking at the circuit I have and have sent and the photos. These are not consistent with each other. We are going to have to do some serious looking.

Firstly I would get rid of all of the paper caps & check any resistors unsolder in the process. Those caps are the light brown waxy ones marked .02mfd etc. and that black AWA one. At the moment I would risk not touching the Electrolytics.

The circuit I sent will show 6J8 as the converter. 6A8 is pin interchangeable, but is not a shortwave valve. If the dial bandspread is out & it has problems on SW, look there.

The 6B6 would have to be a factory mod as their pinouts are not the same & 6SN7 has no top cap The heaters on 6B6 are pins 2 & 7 anode pin 3, Diodes pins 4 & 5. Cathode pin 8. This looks to be right for 6B6. Electrically they are the same valve packaged differently & probably, equally unreliable.

The 6U7 is consistent with a 6U7 not a 6SK7 these are also not pin interchangeable.

I will have another glance through some circuits. It is not uncommon for changes, but I am now left wondering if the model is correct?


Marc.

I almost forgot, the following link leads to a full size image of the circuit diagram.

Image Link

Note previous post unsoldered (typo)

Brad thanks for posting those. Would wonder if it may be an advantage to post a view of the chassis as well?

Marc

No worries there Marc. I'll sort this out tomorrow night when I have access to the database again.

New paperwork issued.
I believe it is actually more like a Rymola 5DMC, Circa 1946
Converter is also 6J8

Marc

G'day Marc, I've forwarded that e-mail as requested. Below are the links to the three images:

Image Link
Image Link
Image Link