Poor Man's Tube Gain Make Up Stage

[mylesgm]

looking great Ian.  I'm sure people should be able to sort out their own brackets and leaving a space for it will be all thats necessary.

 

[strangeandbouncy]

Hi Ian,



  I see you have used IN5007 diodes in the bridge rectifier.


  I canot seem to find them anywhere. Perhaps you meant IN4007 . ..  .


    Kindest regards,


    ANdyP

 

[gemini86]

or rather 1N4007...

 

[strangeandbouncy]

. . . .oops . . .


  still, will 1n4007 do, or is there a reason for 1n5007 . .

 

[ruffrecords]

  still, will 1n4007 do, or is there a reason for 1n5007 . .

My mistake, that should be 1N5407 which you can get from Farnell etc.

In fact the 1N4007 would probably be just fine. The load current is only a few mA so you would have thought a 1A diode would be fine. However, with a capacitor input filter there is a large surge current at turn on as the capacitor initially charges up. How big this is depends on the value of the capacitor, its ESR and the transformer secondary resistance. Now, in mic pres power supplies, I often use 470uF caps and if the transformer secondary resistance plus the ESR of the cap is only 10 ohms then you get a 20A surge current!

Because of this I tend to over specify rectifier diodes in such power supplies so that I have now more or less standardised on the 1N5407. However, looking at the spec of a 1N4007 I see it can take a peak surge current of 30A so it should be fine from that point of view especially as there is no need to use a cap as large as 470uF.

The other thing you have to watch with using large caps is that once the supply is up and running, the diode only conducts for a short time each cycle and and the current through it is many times the load current. Again, with a 470uF smoothing cap and the same assumptions for ESR and transformer series resistance and a load of just 5mA, this peak current is just under 150mA so again it should be well within the capabilities of the 1N4007.

So, on balance, the short answer to your question is yes, the 1N4007 will be fine in this application!

Cheers

Ian

 

[strangeandbouncy]

Hi Ian,


    perfect explanation. Thank you.


    Kindest regards,


        ANdyP

 

[gemini86]

I've never had a 4007 fail on me, even in a 120watt tube amp circuit. Yes I may be stressing their limits a bit, but they're fairly tough little bastards.

 

[MatthisD]

Regarding the output transformer ST5069 mentioned in the first post, apart from being 600/600ohm and 1:1 is it the prefered choice for other reasons or can any high level accepting transformer with the same impedance/ratio do the job?
Matt

(thanks to Ian for the EQ pcbs)

 

[ruffrecords]

Regarding the output transformer ST5069 mentioned in the first post, apart from being 600/600ohm and 1:1 is it the prefered choice for other reasons or can any high level accepting transformer with the same impedance/ratio do the job?
Matt

(thanks to Ian for the EQ pcbs)

The only reason I chose the Sowter 5069 is that I have used it  myself in this circuit and I know it works well and I live in the UK where they are made so they are easy to buy. I would expect any transformer with a similar specification to work.

By the way, apologies for the lack of progress on the PCB for the tube gain make up stage, but I have been rather ill the last few weeks. I had a nasty stomach bug which I think the drugs have finally beaten.

Cheers

Ian

 

[MatthisD]

Thanks for clarifying, there seems to be few options in that case.
all the best,
Matt

 

[Citrus Hill]

Hi Ian,
Please let me know when you have these ready for sale.  I'm thinking about setting my eq's up with a switchable output stage if possible. I'm looking using Pier's ouput stage and putting in an API amp for one output option and then use your Tube stage output as another option.  Once i started dreaming, it's be coming less and less of a "Poor Man" project.    It's my first project that i haven't followed someone else's build or bought a kit, so we'll see how it goes. 
Thanks,
Rob Mc.

 

[ruffrecords]

I have done an updated layout including two output capacitors.  have also moved the heater and HT connection pins in from the edge of the PCB to reduce the risk of shorts if this is used in a 1U enclosure. This means I could no longer route the 0V near the edge of the PCB so I have had to bring it inside the valve socket. This should be OK but if anyone gets worried about it you can easily cut the trace and replace it with a wire link.

I have included four 4mm holes but if everyone is going to be using their own brackets I may well just delete these.

The only thing I need to check is the preset pots. If anyone has any favourites then let me know.

Comments and suggestions welcomed. In the meantime, since the size of the board is pretty much fixed I have check ballpark prices with my PCB supplier and if we order 50 they will cost about 5 GBP each plus shipping.

Cheers

Ian

 

[mylesgm]

I'll definitely be getting two of these but probably 4...

 

[Albrebreton]

Hi Ian, definitely in for three stereo sets.
Cheers.
Alberto

 

[detonator]

a set for 2 channels please

 

[kante1603]

In for two stereo sets please.
Best,
Udo.

 

[Grooveteer]

I'd be in for 4 channels. 

 

[fazer]

Hi Ian,

I'm in for 4.  Very useful board. 

 

[leadbreath]

before i miss the boat again, count me in for 1 x pcb ian

cheers

 

[Hank Dussen]

2 here please!