Sahazel posted while I was composing my post just above this one, so there is some overlap.
-Gnobuddy
-Gnobuddy
Many years ago, I watched a David Attenborough documentary film which mentioned tiny and isolated Anuta Island (aka Cherry Island). The tiny population on this even tinier island had evolved a unique culture over centuries of virtual isolation, in particular, finding many creative ways to efficiently utilize the miniscule amount of land-based natural resources available to them, so as not to destroy their environment, as most other cultures have done.
It was a little glimpse into one of the most unique cultures on planet earth.
Then, a few years ago, I saw a few minutes of much more recent video taken on Anuta Island. The fishermen were now wearing generic made-in-China T-shirts, with the same logos and designs you see on everyone from Americans and Australians to the people of Zanzibar and Zimbabwe.
I wonder if they have a Walmart on Anuta yet. 🙄
-Gnobuddy
They WILL the day they measure what the sales-to-investment algorithm demands.
Today I don´t need Discovery Channel videos on Anuta for that 🙁 : I was born in an agricultural town in the middle of the über-fertile Pampas.
My Father was a Country Doctor and in the late 50s early 60s visited his patients with one or more of us.
We reached some farm, where he checked everybody from the baby he helped deliver a couple days earlier to the black clad Nonna in her 90's.
Some robust Country Mother said: "hey Doctor, you treat your Patients there ... kids!! ... come here!!!"
Depending on time of day, she offered us still warm just milked milk, which left a white moustache on our upper lips, mud oven baked bread, the round large basketball sized type, with a thick crust and huge holes inside, incredibly yellow butter, maybe some homemade jam, or for lunch some Puchero, the all in one meal in a pot THICK vegetables and meat or chicken soup, etc.
Everything and I mean everything, down to clothes washing soap was home made.
Did I mention home made wine which tinted your upper lips deep purple and left a residue in the bottom of the glass or homemade tomato sauce or homemade cheese - sausage - Ham?
Today?
They are fat and fluffy (they were robust and strong in the old days), watching TV all day long, buying everything once a week at some supermarket and even ordering Pizza through some App (not kidding) which is delivered by motorcycle 20-30 minutes later.
THAT, the 10% which still stays there, 90% got bored of Country life and moved to the City.
Oh well.
In any case, not much to do either, not even the Men: instead of regular farming, raising cattle, etc. , everybody have rented their land to some Multinational (think Cargill, etc.) for 100% soybean production (using Monsanto agrochemicals) which is picked by huge science fiction machinery to be sold to the Chinese, hence closing the cycle.
Today I don´t need Discovery Channel videos on Anuta for that 🙁 : I was born in an agricultural town in the middle of the über-fertile Pampas.
My Father was a Country Doctor and in the late 50s early 60s visited his patients with one or more of us.
We reached some farm, where he checked everybody from the baby he helped deliver a couple days earlier to the black clad Nonna in her 90's.
Some robust Country Mother said: "hey Doctor, you treat your Patients there ... kids!! ... come here!!!"
Depending on time of day, she offered us still warm just milked milk, which left a white moustache on our upper lips, mud oven baked bread, the round large basketball sized type, with a thick crust and huge holes inside, incredibly yellow butter, maybe some homemade jam, or for lunch some Puchero, the all in one meal in a pot THICK vegetables and meat or chicken soup, etc.
Everything and I mean everything, down to clothes washing soap was home made.
Did I mention home made wine which tinted your upper lips deep purple and left a residue in the bottom of the glass or homemade tomato sauce or homemade cheese - sausage - Ham?
Today?
They are fat and fluffy (they were robust and strong in the old days), watching TV all day long, buying everything once a week at some supermarket and even ordering Pizza through some App (not kidding) which is delivered by motorcycle 20-30 minutes later.
THAT, the 10% which still stays there, 90% got bored of Country life and moved to the City.
Oh well.
In any case, not much to do either, not even the Men: instead of regular farming, raising cattle, etc. , everybody have rented their land to some Multinational (think Cargill, etc.) for 100% soybean production (using Monsanto agrochemicals) which is picked by huge science fiction machinery to be sold to the Chinese, hence closing the cycle.
Thanks again all for all your replies and insights (don't get me started on large scale industrial / corporate colonisation for now I'll go down another rabbit hole!)
I'm tackling this in short bursts over the christmas rush so excuse the time between drinks but just tested the OT transformer.
Resistance wise it measures as I think it should (40 ohms across primary and 4ohm across secondary) but the actual resistance from primary to secondary does bring in a measurement (all be it a very high one at 20.M ohms).
Gnobuddy I did the reverse signal test as well and I didn't get a step up as you suggested just the same signal level coming from the primary after feeding in 0.3 -0.5 volts at the secondary ... would this suggest its fried?,,,, its definitely passing signal but no step up or down in level.
BTW to me places like this forum and the DIY / salvage community in general offer a real escape or even resistance to the march of everything mentioned above. All this knowledge and sharing of it is gold (courtesy of the internet! : ).
I'm tackling this in short bursts over the christmas rush so excuse the time between drinks but just tested the OT transformer.
Resistance wise it measures as I think it should (40 ohms across primary and 4ohm across secondary) but the actual resistance from primary to secondary does bring in a measurement (all be it a very high one at 20.M ohms).
Gnobuddy I did the reverse signal test as well and I didn't get a step up as you suggested just the same signal level coming from the primary after feeding in 0.3 -0.5 volts at the secondary ... would this suggest its fried?,,,, its definitely passing signal but no step up or down in level.
BTW to me places like this forum and the DIY / salvage community in general offer a real escape or even resistance to the march of everything mentioned above. All this knowledge and sharing of it is gold (courtesy of the internet! : ).
I think that a dc resistance of 40 Ohm for the primary is suspiciously low. I would expect something like 200 Ohm or more. So it could well be that the primary is shorted.
Thanks PFL200 and I guess combined with the lack of step up when fed a signal backwards it would make sense that there is a short.... also could possibly account for the small distorted signal taken at the pentode being directly attached to the OT primary ?
Like PFL200, I'm suspicious of those values. The primary resistance seems a bit low (too good to be true), and the secondary resistance quite a bit too high - the actual DC resistance of the secondary would normally be much lower than the nominal 15-ohm speaker impedance.
Unfortunately, that is bad news. The schematic you posted shows a 7000 ohm primary impedance, and 15 ohm secondary impedance. Dividing those gives you the impedance ratio, which is nominally 466.67. The winding ratio is the square-root of the impedance ratio, which works out to nominally 21.6:1.
So if all was well, you would be seeing roughly 20 times as much voltage across the primary, compared to the voltage across the secondary. 🙁
It would seem the transformer has moved on to the great scrapyard in the sky, and unfortunately, audio transformers tend to be expensive and hard to source, particularly in Australia, from what I've read on the Aussie Guitar Gearhead forums.
That said, there are at least three options to consider:
1) If there is a transformer rewinding business still operating near you, they might be able to rewind your OT. The odds of a small-transformer rewinder still being in business are slim, but you never know.
2) If you have a sufficiently large wad of cash to fling at the problem, there are still OTs made by Hammond (Canada), and various Chinese companies (Triad, for one), and hopefully you will find one close enough to your requirements.
The original 7000 ohms : 15 ohms ratio of your OT is the same as 3733 ohms:8 ohms. 4000 ohms:8 ohms is probably close enough; that might be available off-the-shelf from the above suppliers.
If you can find a suitable 4k:8 ohm SE guitar output transformer, you'll want a single-ended one, rated for at least as many watts as your Goldentone puts out. I estimate that at close to 5 watts, based on the nominally 309V power supply voltage, and the nominally 7000 ohm transformer primary impedance.
3) Saving what might be the best for last, a couple of smart Australians pioneered the idea of using relatively inexpensive "100 V audio line transformers" as valve guitar amp output transformers. Paul Cambie and the same Roly Roper we mentioned earlier were part of this, and Roly had a page on his website where he discusses the math behind it: https://ozvalveamps.org/optrans.htm
Now, you have a single-ended amp, and these are not supposed to work well with an inexpensive audio line transformer (which is not designed to tolerate standing DC current through it's primary). That said, on the AGGH forum, I have read of other Australians who pushed on where engineers fear to tread, and found that using an audio line transformer in a SE amp did actually work, particularly if they used a transformer that was oversized for the job, allowing it to better tolerate the DC anode current.
I have gotten away with something similar myself, though in my case, I used a push-pull OT capable of several watts with a tiny single-ended amplifier putting out only about a quarter of a watt; the far-too-big transformer coped very comfortably with the very small standing DC current.
I just did the maths, and - if you are actually using a 15 ohm speaker - what you want is a 100V audio line transformer with a 1.5 watt tap; that will provide nearly the same 7000 ohm: 15 ohm ratio as your now-deceased stock output transformer.
One of the things I don't know is whether it is easier for you to source 70 V or 100 V audio line transformers in your corner of the world. As far as I know, 100 V was the old Australian standard - but the US standard is lower, at a nominal 70.7 volts, and perhaps Chinese-made, US-standard "70 V" audio line transformers are now easier to find than 100 V ones in Australia? (Yet another little bit of cultural homogenization?)
If you get back to me with (a) your actual speaker impedance (4 ohm? 8 ohm? 15 ohm?), and whether you have access to 70 V or 100 V audio line transformers, I can help you figure out the appropriate audio line transformer tap that is most likely to work for you.
I agree with you entirely. In a world increasingly tuned to endless blind consumption (rather than creation), it's wonderful that the few remaining people who still make, modify, or repair things for themselves, are able to support each other in this way.
-Gnobuddy
Yellow Cab, have you got another meter to cross-check any measurement of Vac or resistance you make, or have a known resistor or a known Vac supply to confirm values?
Depending on where you are located, you may be able to get a replacement Rola output transformer from someone nearby with a bit of flag-waving your need - such as from an AGGH or HRSA member. I have spare 7k:2.3 and 7k:8 SE OPTs of circa 5W as 7k SE was common for 6M5 as well. As Gnobuddy indicates, a line transformer from say Jaycar may suffice as an interim measure - they are typically 8R output, but you can use a 15 ohm speaker and just double the input impedance, but need to check some forum posts to work out what taps to use for the models on the shelf - however they weren't specifically made for SE operation with DC bias so they are not exactly the part you are after.
Depending on where you are located, you may be able to get a replacement Rola output transformer from someone nearby with a bit of flag-waving your need - such as from an AGGH or HRSA member. I have spare 7k:2.3 and 7k:8 SE OPTs of circa 5W as 7k SE was common for 6M5 as well. As Gnobuddy indicates, a line transformer from say Jaycar may suffice as an interim measure - they are typically 8R output, but you can use a 15 ohm speaker and just double the input impedance, but need to check some forum posts to work out what taps to use for the models on the shelf - however they weren't specifically made for SE operation with DC bias so they are not exactly the part you are after.
I already did the maths. The closest tap is 1.5 watts, for a 100-volt audio line transformer intended to have an 8 ohm speaker, but actually connected to a 15 ohm speaker. Primary impedance is nominally 6667 ohms in this case.
If there were such a thing as a 1.4285 watt tap on a 100V line transformer, designed for an 8 ohm speaker but actually connected to a 15 ohm speaker, then it would provide exactly 7000 ohms primary impedance. But a 1.5 watt tap is more likely to actually be available.
Not knowing anything about Australian suppliers, I couldn't go any further until trobbins mentioned Jaycar. I checked the Jaycar website, and found only one audio line transformer listed. It's rated for 5 watts into an 8 ohm speaker, and can be used with either 100 V or 70.7V audio line voltage. It does not have a 1.5W tap, but does have 1 W and 2 W taps. Fortunately, these are close enough to do the job.
Keeping it simple: If you (Yellow Cab) want to try using this Jaycar transformer, and are using an 8 ohm speaker, connect "C" (the 100 V primary end) to B+, and the 1 W tap to the pentode's anode. The 8 ohm speaker goes in the usual place, across the transformer output.
If you're using a 15-ohm speaker, connect "C" to the B+ voltage, and the 2 W tap to the pentode's anode (instead of the 1 W tap).
In both cases, the pentode will "see" a 10k load. It's not exactly 7 k, but the difference is small enough not to matter in any significant way for the present purposes.
The unknown is how well this little 5W transformer will cope with the standing DC anode current of the pentode. It would have been nice to have a higher-wattage audio line transformer, but Jaycar doesn't list such a thing.
-Gnobuddy
Attachments
Jaycar have supplied quite a few different line transformer models over the years, so it's pot-luck as to what is presently stocked. I have five of those MM1900, as it provides a neat 20k:8 PP at nominal 5W for small amps.
Although the MM1900 has the same turns from C to 2W as for 2W to 0.5W (and hence is conveniently used for a PP OPT), the turns from C to 1W (which presents 10kohm Z) is a little different to the turns from 5W to 0.5W, which presents about 9k3ohm for 8R.
Hopefully there is no noticeable difference when used for SE. The main aspects to note are that using a winding segment with less turns will bias the BH curve less for the same idle dc current, but would also provide the least primary inductance for low-frequency response.
Although the MM1900 has the same turns from C to 2W as for 2W to 0.5W (and hence is conveniently used for a PP OPT), the turns from C to 1W (which presents 10kohm Z) is a little different to the turns from 5W to 0.5W, which presents about 9k3ohm for 8R.
Hopefully there is no noticeable difference when used for SE. The main aspects to note are that using a winding segment with less turns will bias the BH curve less for the same idle dc current, but would also provide the least primary inductance for low-frequency response.
I found this little DIY build online, a tribute to Yellow Cab's Goldentone one-valve 6GW8 amplifier: http://www.thecolonel.id.au/index.php?p=1_12
There is a link to a You Tube video demo of this amplifier at the very bottom of the above page:
The introductory text for that video states that this amp was built "...using the chassis and transformers from a vintage HMV record player". So, unfortunately, this particular build provides no link to a suitable currently-available off the shelf OT.
As for the circuit, the 20nf (!!!) cap across the input seems a bit much - I would expect a very dull tone from this DIY amp.
Given that the video shows a Telecaster, which is a famously bright guitar, I would say the sound from the demo video confirms this. A less-bright guitar, such as any Gibson-style guitar with humbuckers, is really going to sound dull.
There are better ways to deal with instability than dumping a huge cap across the guitar input, such as careful lead dress in the build, taking particular care to keep wiring to the OT primary as far away from the input wiring as possible. If all else fails, it would be better to put the low-pass cap anywhere other than at the input.
On the other hand, the input stage has been converted to self-bias (rather than the original troublesome grid leak bias), which I think is entirely a step in the right direction.
-Gnobuddy
There is a link to a You Tube video demo of this amplifier at the very bottom of the above page:
The introductory text for that video states that this amp was built "...using the chassis and transformers from a vintage HMV record player". So, unfortunately, this particular build provides no link to a suitable currently-available off the shelf OT.
As for the circuit, the 20nf (!!!) cap across the input seems a bit much - I would expect a very dull tone from this DIY amp.
Given that the video shows a Telecaster, which is a famously bright guitar, I would say the sound from the demo video confirms this. A less-bright guitar, such as any Gibson-style guitar with humbuckers, is really going to sound dull.
There are better ways to deal with instability than dumping a huge cap across the guitar input, such as careful lead dress in the build, taking particular care to keep wiring to the OT primary as far away from the input wiring as possible. If all else fails, it would be better to put the low-pass cap anywhere other than at the input.
On the other hand, the input stage has been converted to self-bias (rather than the original troublesome grid leak bias), which I think is entirely a step in the right direction.
-Gnobuddy
Thanks again Gnobuddy and trobbins really appreciated.
Hope all had a good (or some kind of) break over Christmas.
Will check out the above next time I'm at Jaycar but before I go down that route I did actually see a ROLA 5w (rated for maximum 10watt) OT on ebay hand wound in South Australia and from what I can tell they seem ideal for this purpose with the 6gw8 listed among other compatible valve types at the output stage.
I"m a little unsure whether they handle the HT of 300+ volts but am checking on that. They are listed as 'medium fidelity' as well but for a guitar amp like this one I'm sure that is plenty looking at the frequency response.
Anyway specs listed below in case anyone has any thoughts.
5K (Primary) to 4 and 8 ohms (Secondary) (PS the hi flux speaker in my amp measured at 12ohms when disconnected).
Core material - Japan GOSS
Bobbins - preformed high impact plastic
Wire - Rola and Philips Magnet wire
Finish - dipped in transformer varnish and low baked
leads - 18mm PVC covered
Primary leads impedance 5K
HT - RED
Anode - Green
Secondary leads
common - black
4 ohm tap - yellow
8 ohm - blue
Impedance ratio 625:1 turns ratio 25:1
nominal voltage across primary 158V RMS
nominal voltage across secondary 6.325V RMS
Primary Inductance 29H
Nominal power 5W RMS
Maximum power 10W RMS
Frequency Response 20hz to 20khz +/- 3db
Nominal DC primary current 60ma
Size
H - 50mm W - 60mm D - 50mm
stack - 28mm
mounting centres - 72mm
mounting flange width 85mm
Suitable valve types
6BW6, 6V6, 6AQ5, 6BM8, 6GW8, 6BQ5
6L6, EL34. 807, 2A3,
Hope all had a good (or some kind of) break over Christmas.
Will check out the above next time I'm at Jaycar but before I go down that route I did actually see a ROLA 5w (rated for maximum 10watt) OT on ebay hand wound in South Australia and from what I can tell they seem ideal for this purpose with the 6gw8 listed among other compatible valve types at the output stage.
I"m a little unsure whether they handle the HT of 300+ volts but am checking on that. They are listed as 'medium fidelity' as well but for a guitar amp like this one I'm sure that is plenty looking at the frequency response.
Anyway specs listed below in case anyone has any thoughts.
5K (Primary) to 4 and 8 ohms (Secondary) (PS the hi flux speaker in my amp measured at 12ohms when disconnected).
Core material - Japan GOSS
Bobbins - preformed high impact plastic
Wire - Rola and Philips Magnet wire
Finish - dipped in transformer varnish and low baked
leads - 18mm PVC covered
Primary leads impedance 5K
HT - RED
Anode - Green
Secondary leads
common - black
4 ohm tap - yellow
8 ohm - blue
Impedance ratio 625:1 turns ratio 25:1
nominal voltage across primary 158V RMS
nominal voltage across secondary 6.325V RMS
Primary Inductance 29H
Nominal power 5W RMS
Maximum power 10W RMS
Frequency Response 20hz to 20khz +/- 3db
Nominal DC primary current 60ma
Size
H - 50mm W - 60mm D - 50mm
stack - 28mm
mounting centres - 72mm
mounting flange width 85mm
Suitable valve types
6BW6, 6V6, 6AQ5, 6BM8, 6GW8, 6BQ5
6L6, EL34. 807, 2A3,
I did, indeed - and it was a very welcome break from work.
Omicron-variant COVID-19 cases are starting to pile up here, and we have significant new legal restrictions in place in British Columbia, so it was a quiet Christmas, just myself and my wife "alone together". But if I have to have only one person for company in a world gone upside down, she's the one I would pick anyway. I'm very thankful we still have each other.
Most likely it will. The OT you're looking at was designed for use with an output valve, so B+ in the range of hundreds of volts would have been expected.
The data included "158 volts RMS", which translates to roughly 223 volts peak, or 450 volts peak-to-peak. That's in the right ballpark - with a 300 volt B+ and, say, 50 volts anode-to-ground when turned fully on, you could in principle get 500 clean peak-to-peak volts across the transformer primary.
As an aside - the cheap 100-volt audio line transformer we were discussing earlier is only really intended to be used with a 100-volt RMS primary voltage, but many of your countrymen have already proved that they do hold up to typical low-power valve guitar amp B+ voltages.
Your oddball (in 2021) speaker impedance will throw a wee spanner in the works, but not an unsurmountable one. More like throwing a ripe orange in the works rather than a spanner, actually.
The nominal (AC) impedance of a speaker is always higher than the DC resistance of the voice coil, typically by very roughly a third. For example, a roughly 3 ohm DCR usually means a nominally 4-ohm speaker.
The 12 ohm DC resistance you measured, therefore, does indeed suggest a nominal speaker impedance of maybe 15 or 16 ohms, just as the old schematic you posted suggests.
Definitely avoid using the 4-ohm tap. That is a huge mismatch for your purposes.
However, the 8-ohm tap is usable. if you connect your 15-ohm speaker to the 8-ohm tap (i.e. speaker to black and blue leads), the primary impedance will rise proportionately, in other words, from 5 k to the new value (5k x (15/8)). That works out to 9.4 k.
While this is higher than the nominal 7k you want, it's not sufficiently higher to cause a problem. Nothing about a simple valve circuit like this one is all that fussy, and your amp will work just fine with the nominally 9.4k primary impedance. (There might be very slight changes in overdriven tone, but it's unlikely that this will be sufficient to cause you grief, and maybe not even enough to notice at all.)
If, for purely OCD (obsessive compulsive disorder) reasons, you really want that nominal 7k primary impedance, there is a simple, if slightly inelegant, workaround. Put a power resistor in parallel with your 15-ohm speaker to reduce the combined resistance a bit, so that the 25:1 winding ratio ends up presenting a 7000 ohm primary load.
I did the math, and a 47 ohm power resistor wired in parallel with the 15 ohm speaker will come very close. (A 43 ohm resistor comes even closer, but that value only exists in E24 series resistors, and is likely to be harder to find. There won't be any worthwhile change, anyway.)
The 47 ohm resistor will steal about a quarter of the output power of the amplifier. If 4 watts comes out of the transformer secondary, the resistor will steal roughly one watt. This will reduce maximum loudness very slightly, but it is a small enough change to be hardly audible (less than 3 dB).
That tells us the 47 ohm resistor may have a watt or so to deal with, so it needs to be sufficiently beefy to cope with that. At a minimum you want a 2-watt resistor, but 2 W resistors run very hot if you put 1 watt into them. Power resistors tend to be quite inexpensive, so I would suggest using a 5-watt part instead. That will cope very comfortably with anything this amplifier might ask of it.
So there you are. Wire your 15-ohm speaker to the 8-ohm taps, and you're good to go.
And if you happen to be feeling extra-picky that day, wire a 47 ohm, 5 watt, resistor in parallel with the 15 ohm speaker, and you'll be all set.
-Gnobuddy
It sounds like the OPT is a cloned newly re-wound part? If so then I'd anticipate the maker has confirmed the insulation resistance of the primary winding to core, and to secondary, with at least 1kVdc - imho you should ask if it is a 'new' winding and if it was tested for insulation withstand and to what voltage.
It appears that the 'maker' can use a calculator, but sadly tried to portray the secondary voltage as 6.325Vrms, but should have just used 6.3V. But that does beg the question as to whether the 29H primary inductance was measured at 60mAdc and at what Vac rms level (as the inductance could well vary a lot if tested at say 1Vrms versus 100Vrms).
It appears that the 'maker' can use a calculator, but sadly tried to portray the secondary voltage as 6.325Vrms, but should have just used 6.3V. But that does beg the question as to whether the 29H primary inductance was measured at 60mAdc and at what Vac rms level (as the inductance could well vary a lot if tested at say 1Vrms versus 100Vrms).
Another option if you are willing to put your speaker on an 8ohm tap is an epiphone valve jr output transformer. They have a 7k primary and if you put the call out on a few forums, including AGGH you may snag one cheaply as during the valve jr craze many people experimented with changing them out.
That's an interesting option!
I found an ad for a (OEM, used) Epiphone Jr. output transformer on Reverb.com (picture attached). The label says 5.4k primary impedance.
With a 15 ohm speaker connected to the 8 ohm tap, that should rise to nominally just above 10k.
-Gnobuddy
Attachments
That one actually has a 16ohm secondary as well. 5.2k primary won’t make a huge difference. I’m sure I’ve seen 6gw8 single ended schems with 5k primar. That would be one of the series 3.
It seems to me the OT is a fairly standard one, you will find these in old tube radio sets or old reel to reel recorders. Here in europe you can find these for next to nothing. especially if they don't work anymore. I think it is good fun and planet friendly to recycle these old devices.
You are lucky!
In North America, the era of tube radios and reel-to-reel tape recorders ended many, many decades ago - about six decades ago! In bigger cities in North America, people don't have such settled lives, where grandpa's or great-grandma's tube radio is still in the attic of the family house.
More likely grandma and grandpa's belongings were thrown in the trash long ago, as there is no attic and no family house, only a string of small and expensive rented apartments, with a few years living in each one, before yet another move to yet another apartment.
In the cities in which I've lived (both in the USA and Canada), old tube electronics are quite rare, and when you do find something for sale, it's priced absurdly high, much more than the cost of a brand-new output transformer from Hammond.
Another Canadian member of this forum - living on the opposite coast, in an area with many smaller towns and more rural communities - has a very different experience. He seems to constantly find amazing old tube equipment at absurdly low prices. I'm guessing people have stabler lives there, and many people still have a family home in which they and their older relatives have lived for generations.
No such luck in my area!
I have no idea what the availability of old valve (tube) equipment is like in the OP's corner of Australia.
-Gnobuddy