Aussie Made Stuff Score #2

[TIMBO]

This one is a local made (Brisbane,Australia) MUSIC MASTERS RADIO.(1954)
The timber cab was stuffed but the amp/radio looks to be in good condition
1X 6av6
1X 6aq5
1X 6an7
1X 6ba6
1X 5y3gt

This one is clean inside and out, but it looks like the cockies have been chew'n on ot OT but it looks to be OK.
This one i think that i might purchase another 6aq5 and may be do a PP if the tranny has enough juice.
I did find some info on this one and looking at the chassis it appears that it may have a PP version (extra tube holes)

It seems that the 6AQ5 was popular for these low watt amps and they sound pretty good.Thanks

I think the 6ba6 can be used,so if anyone has any ideas

Just found this,sounds great http://www.marshallforum.com/other-amps/47675-10w-6aq5-tmb-amp.html

[HotBluePlates]

This one i think that i might purchase another 6aq5 and may be do a PP if the tranny has enough juice.

I wouldn't count on it, unless you know for sure the PT is the exact same as the one in the push-pull version. There really wasn't enough profit margin in small radios like this to over-build anything.

I think the 6ba6 can be used,so if anyone has any ideas

It's a good tube if you want to make a compressor, otherwise it might not be too helpful.

The 6BA6 is a remote-cutoff tube. It was used in radio-frequency (RF) or intermediate frequency (IF) stages to allow an automatic volume control (AVC). In simple terms, it made far away, weak stations have the same volume as nearby, strong stations.

It does this by having a different amplification at low-bias levels than at high-bias levels. The needed change in bias voltage for different-amplification is generally bigger than the signal to be amplified. Instead, a sample of a later stage's audio is rectified and filtered to make a d.c. voltage. Big signals create big d.c., which is fed back via the AVC circuit to the 6BA6. That changes the bias of the tube to result in less amplification. Small signal create small d.c., which the AVC feeds back to result in less bias and more amplification.

I keep threatening to put this in a guitar amp, but I'm not sure it will do a better job than a compressor pedal, which will probably cost the same (or maybe less, used) as the parts needed to create a "guitar AVC". That, and the pedal can be used on any amp, where the 6BA6 is stuck in its one amp. And the fact I'm not convinced I need a compressor pedal.

And, of course, the 6BA6 is used in a piece of VTVM calibration gear I own, so I'd rather save my 6BA6's for that rather than waste them in an amp... 

[TIMBO]

Hi guys, Taking a break from my other build,so i thought i cut away the crap and see if there is any thing usefull in here.
E caps are DUCON 16uf and 8uf @525v cardboard exterior and look to be in good order (nothing oozing) Australian made.
Other caps are DUCON "high-seal" also look to be in good order
Several brown rectanglar things that have SIMPLEX SM and one smaller with SIMPLEX P/T 
Choke in good condition (just some of the outer tape the rochers have chewed on) looks like 14H volts unknown and 550 ohms
OT SE and got 5000 stamped on the top and July 1954 on the side

The PT looks in good order it might have enough juice if i am reading it right :-
The info tells me that the rect tube is a 5Y3 (not marked on the tube)
5V tap to pin2
385v tap to pin4
CT
385v tap to pin6
2A to pin8 (i'm thinking that PT HT rated @2A????
Earth tag
6.3v tap
3A tag connected to chassis (heaters rated @3A????
I think i have plenty to play with those kinds voltages/current so i thinking of a Blues Trainwreck build using a pair of 6aq5s and i been told that a 100v line transformers make good OTs. Any input would be great. 

[darryl]

The transformer looks like a Henderson - they were a very common brand in Australian equipment of that era. They generally used the standard tagboard layout you have pictured.

The 240 volt primary winding is between 'C' and '240'. There are other vacant points labeled '220' and '260' which were available for transformers with multiple primary voltage taps.

The secondaries are:  1.  285-CT-285   570 volts with centre tap to supply the HT at unknown current.
                              2.  5V-2A           5 volts at 2 amps which would typically supply a 5Y3 heater.
                              3.  6.3V-3A        6.3 volts at 3 amps to supply the remainder of the valve heaters.

I'm not sure what winding the 'E' tag connects to - it will have to be checked with an ohm meter.   

If the filter choke is electrically intact, it will probably be OK. Likewise the single-ended output transformer. Although it has a 5000Ω primary, it may be only a 2Ω secondary. Two ohms was the most common speaker impedance in that era.

The power transformer and the filter choke would have been rated for exactly the job they were doing - there would not be additional power margin built in for a push-pull amplifier.

All of the Ducon cylindrical capacitors should be discarded. The large electrolytic capacitors will have dried out, and their failure under load would endanger the rectifier valve and the power transformer. The smaller waxed paper capacitors will very likely be leaky, and even if still functional, could never be trusted.

The Simplex blocks are mica capacitors, which will probably be fine. They should still be measured though.

There are a couple of carbon composition resistors in your pictures - they should be measured, and if they are within their ( usually ) 20% tolerance you *might* consider re-using them.

[TIMBO]

Thanks Darryl, Yes, it is a henderson.The "E" tag is connected to the chassis along with the "3A" tag could it be an earth screen in the transformer??

I was only ASSUMING that this could support a PP by the guesstimate current draw of the existing tubes (approx 80mA) and the heaters (165mA). The new line up i was thinking would add up to approx (2x6aq5 and 3x12a_7) being about 90mA and 180mA for the heaters and if the tag board is marked as 3A,the heaters would be fine and the radio part i would think would draw more than 10mA, YES/NO????
The tag board i am sure is marked as 385-0-385
The PT output is a lot higher than i would expect, when the the max rating of the 6aq5s is 250v (have seen up to 300v) but maybe the radio part needs a higher voltage.
Would the 5Y3 pull the output down enough by itself ??? and will it limit the current as well ???

Is there a way to measure the current output of this PT. Thanks

[smackoj]

Hoorah, I got the answer to my question about what those square plastic thingies do without even asking. Thx darryl

 

[darryl]

Yes, it is a henderson.The "E" tag is connected to the chassis along with the "3A" tag could it be an earth screen in the transformer??

The wire link from 'E' to '3A' will have to be removed, so the 'E' tag can be checked for continuity to any other tag.

The tag board i am sure is marked as 385-0-385

You will have to check this when you eventually apply power to the transformer. Radios of that vintage which used field coil loudspeakers generally had 385-CT-385 transformers, to allow for the voltage drop in the field coil. Newer radios with permanent magnet speakers used a 285-CT-285 transformer. The label on your transformer appears to be 385 overstamped with 285. Many Henderson transformers from that period were overstamped - they must have had thousands of those tagboards already labeled 385, which they re-labeled 285, for use in lower voltage transformers. ( For those newfangled permanent magnet speakers, and 250 volt miniature valves like 6AQ5's. )   

Is there a way to measure the current output of this PT.

No.      I would guess its DC current capability to be about 50-60mA.

Some of your heater current calculations don't seem to be correct.  Two 6AQ5's and three 12AX7's would require 2 x 0.45A + 3 x 0.3A = 1.8A  This is well within the 3A rating of the transformer, but I still seriously doubt if it would have the HT current for push-pull 6AQ5's.