"Superfly" - submini tube version of Doug H's Firefly

[makaze808]

Use the 6111wa output tube and use 4-5k primary impedence when working out the tranny connections as stated earlier, it works a treat..

Highly recommended project.    

[makaze808]

This output transformer is mentioned several times

  http://uk.rs-online.com/web/search/searchBrowseAction.html?method=retrieveTfg&binCount=1&Ne=4294957561&Ntt=oiutput+transformer&Ntk=I18NAll&Nr=AND(avl:uk,searchDiscon_uk:N)&Ntx=mode%2Bmatchallpartial&N=4294955308&Nty=1

Can this be dropped into the superfly replacing the 125a  wihtout any mods to the circuit?

[misterg]

This output transformer is mentioned several times

  http://uk.rs-online.com/web/search/searchBrowseAction.html?method=retrieveTfg&binCount=1&Ne=4294957561&Ntt=oiutput+transformer&Ntk=I18NAll&Nr=AND(avl:uk,searchDiscon_uk:N)&Ntx=mode%2Bmatchallpartial&N=4294955308&Nty=1

Can this be dropped into the superfly replacing the 125a  wihtout any mods to the circuit?

I would say yes. I used one for my original Firefly and for testing my sub-mini version, but reverted to the 125A for cosmetic reasons. In fact, IMHO it's a better sounding transformer than the 125A (YMMV!), but is physically a bit bigger. I've got one in my current 4-4-0 build, and it sounds grand.

You will need to choose the correct taps for the output impedance you want.

For info, I measured the turns ratios of the RS transformer as follows:

Primary connections 1 and 4 (2 is the centre tap)

Secondary
D-C 67.2:1
C-A 57.6:1
D-B 44.8:1
D-A 31.0:1

Primary connections 2 and 4 (3 is the centre tap)

Secondary
D-A 15.6:1

Primary tap 2 forms a centre tap between 1 and 4, and tap 3 forms a centre tap between 2 and 4. the 1-3 primary tap is no use for the firefly, because there is no corresponding centre tap, but the ratios are :

Primary connection 1 and 3 (N.B. No centre tap)

Secondary
D-C 50.0:1
D-B 33.3:1
D-A 23.1:1

To calculate the output impedance (in case you don't know) multiply your speaker impedance by (turns ratio) squared.

For example taps 1 & 4 on the primary with C & A on the secondary gives a turns ratio of 57.6:1 , so an output impedance for an 8 ohm speaker of:

8 x 57.6 x 57.6 = 26,542 ~ 26.5 k ohm

With this transformer in the original Firefly I used primary taps 1, 2 and 4, with D-C, C-A and D-B for 4, 8 and 16 ohm outputs respectively.

Going for lower impedances made it louder but harsher (again, YMMV!)

To clarify: You would connect B+ to terminal 2, and the anodes of the "power" valves to terminals 1 and 4 respectively, then choose the secondary terminals depending on your speaker impedance. You won't break anything by going for ~20 - 25k output impedance to start with (i.e 8 ohm speaker to terminals C and A).

Andy

[makaze808]

Thanks for that reply, very help full.

[frankm]

Hi guys, do you think this amp will work fine with two 6021 submini tubes? 

[frequencycentral]

Hi guys, do you think this amp will work fine with two 6021 submini tubes? 

You should be able to do this. Just a couple of things to bear in mind regarding the preamp tube. 6112 has a gain of 70, 6021 has a gain of 30 (or 35, I forget), so you won't be pushing as much. This may be desirable and may actually make for a slightly cleaner, slighly quieter amp. You may want to change the two anode resistors (R12 and R13) to correctly bias for 6021, maybe socket them and experiment with 47k or 68k instead of 100k. May also be worth socketting the preamp 6021 so you can replace it with a 6112 at some point if you wish. I use SIL strips to sockets these subminis.

[Beros]

Just built one. Could really need some help.

Insead of it working, it makeas a beeping sound that changes when i turn the pot. Seems to be comming from the circuit itself or maybe the power supply...
Both tubes are glowing. Heat sink does get hot..

And, oh yeah, i put an 430 R resistor as R1, but that should'nt matter, should it?

I think i just fried something. I was measuring the voltage on the transformer center tap, and may have shorted something. Saw a spark and now the voltage reads 57 volts. Is it the IRF740 thats toasted?

[frequencycentral]

With the ones I've built I can dial in higher voltages than 185v, so I'd be concerned about the voltage multiplier section. But you're getting HV so it's not all bad. The key part here would be the inductor, I've tried other inductors than the I usually use without any luck. Also, what's the spec of the 12v adapter you're using? Is the unit passing any sound? Got any photos of both sides of the board? Tubes in the right way round?

BTW, I *think* that 430R shouldn't matter - but it's not a 430k is it?

[Beros]

With the ones I've built I can dial in higher voltages than 185v, so I'd be concerned about the voltage multiplier section. But you're getting HV so it's not all bad. The key part here would be the inductor, I've tried other inductors than the I usually use without any luck. Also, what's the spec of the 12v adapter you're using? Is the unit passing any sound? Got any photos of both sides of the board? Tubes in the right way round?

BTW, I *think* that 430R shouldn't matter - but it's not a 430k is it?

No it's not a 430k.
No sound at all. It makes weird beeping noises comming from the circuit itself, not the speaker. Sounds different when i turn the pot or play a note. Still no sound from the speaker.

Uhm, i think i just fried or shorted something with my multimeter.. Now the center tap just rads about 50v...
The inductor is a 100uH radial one, similar looking to the one you use. Got it cheap from ebay.

The weird beebing noise when i turn the volume pot bothers me.. Thats not normal, is it?
Tubes are the right way around. Photos:

[frequencycentral]

That PCB look different to my layout, particularly around the trimmer? If you shorted something it may blow the MOSFET or the inductor. Some of your caps are HUGE!

[Beros]

That PCB look different to my layout, particularly around the trimmer? If you shorted something it may blow the MOSFET or the inductor. Some of your caps are HUGE!

Yeah, I modified your layout since i got a smaller sized trim pot.
Had some orange drops laying around.

Changed inductor and the UF4004 (that's where the spark came from). Still 50-someting voltage on the transformer center tap.

Tomorrow I'll change the mosfet.
I've been going through the pcb over and over, and it's driving me nuts. Can't find whats wrong.

The power supply is 12V 500mA.

[makaze808]

Beros that soldering don't look to good to be honest...

[Beros]

Beros that soldering don't look to good to be honest...

I'm a guitar player. It's ok.

[theundeadelvis]

Beros that soldering don't look to good to be honest...

I'm a guitar player. It's ok.

I think your soldering is fine. Sure it's not the neatest out there, but as long as there's no solder bridges or cold solder joints you should be fine. I would drag a pick through the negative spaces to clear out some of the flux and be sure there's no hard to see solder bridges. Also, look for any dull solder joints, as this can be a sign of cold joint that may need reflowed. The more you solder, the cleaner things will get. Good luck!

[Taylor]

Sadly, even guitar players are not free of the bonds of physics. Even Jimi could not coax a tone out of an amp with solder bridges.

[Beros]

There were no solder bridges..

I just forgot to connect the transformer to ground. 
Well, I have sound. But I'm not free from trouble yet...

It's choppy and sounds weird.. Like a bad tremolo.

Transformer measures 70 volt.. Hmm...

[Beros]

There were no solder bridges..

I just forgot to connect the transformer to ground. 
Well, I have sound. But I'm not free from trouble yet...

It's choppy and sounds weird.. Like a bad tremolo.

Transformer measures 70 volt.. Hmm...

Never mind... I think a new mosfet will do the trick.

[misterg]

There were no solder bridges..

I just forgot to connect the transformer to ground. 
Well, I have sound. But I'm not free from trouble yet...

It's choppy and sounds weird.. Like a bad tremolo.

Transformer measures 70 volt.. Hmm...

Never mind... I think a new mosfet will do the trick.

The mosfet must be doing something if you're getting 70V

I would suggest trying a different power adaptor before doing anything else - preferably a 1 amp *transformer* based one (i.e. the heavy type). Some switch mode power adaptors (i.e. the light type) don't react well to supplying the switching converter in this circuit. It will draw >600ma steady, but with much bigger spikes, and this sometimes seems to 'fight' with the regulation in the power adaptor.

HTH

[tominator]

Hey guys. I'm fairly new to the form and effect/amp building in general. Anyway I decided to be ambitious/stupid and attempt to build this sub-mini amp sometime in the near future and therefore I have been sourcing parts for this build. It seems that one of the hardest item for people to find is the 7327 tubes and I appear to have found someone who has a stash of them. I was surfing ebay and was that member chillo0 was selling some tubes he bought at a government auction, but in a lot with some 67 tubes total. I emailed him asking if he had some 7327s he could sell me to which he replied he had "lots." Long story short he sold me 3 tubes for $21 shipped, which seemed quite reasonable to me. When I got them they were well packaged and in good condition, new in the box. So if anyone out there needs a 7327 tube you could try looking him up.

Here's a link to the origional auction I found:
http://cgi.ebay.com/6T8A-6K6GT-CRC-5693-67-tubes-total-all-new-/5870527185?pt=Vintage_Electronics_R2&hash=item15de922d1

[frequencycentral]

Another on the way: