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barackuda 9th April 2011 03:07 PM

S5 K8-LM mono KIT (total newbie)
My name is Danny, been a little active in the speaker forums.
I have BiBs with Fostex 168 sigmas (i love em) and want to build my first tube amp.
I have some experience in electrics, but i'm not counting on it. Started to read about the tubes and safety and the lot.
I've ordered the two monoblocks from S5 without the transformers (too heavy to ship to europe). I got the specs for them. I've been looking for the Hammond trans (read somewhere that they are good replacement-upgrade to stock). Perhaps I didn't done enough reading, but I cant find any that match the specs.

My questions :) :
- has anyone build this kit?
- what replacement transformers? (i know, i will have to get into the theories)
- if yes, what part number for Hammond? (available in UK)
- what mods to upgrade the bass response? (i read that they lack in this region)
- what mod (description) to discharge the amp after power off? (safety, small children)

I will make a proper chassis for it, that is sure.

Please don't stone me for these questions, I'm just starting with amps :headbash:


P.S.: any, I mean really ANY suggestions are highly appreciated.

mashaffer 9th April 2011 05:17 PM

I haven't built one but...

Is it this one?

Model 8LS Stereo Integrated Tube Amplifier

If so it looks like it uses these for output tubes.

Just based on the data sheet it looks as though it likes about 10K ohms plate to plate on the output transformer primary.

What specifications did they give you on the transformers? Do you have the schematic yet?

barackuda 9th April 2011 05:33 PM

Hello mashaffer
thanks to chime in.
its this one :
actually two :) the specs for the trans are:
Output Transformer =
Ratio 35 : 1
Primary Resistance 400 ohms
Secondary Impendence 8 ohms
Power 10 watts
Power Transformer =
120 / 220 VAC in
180VAC @ 0.250ma Secondary #1
6.0 VAC @ 5.5 A Center Tapped Secondary #2

I'm pretty sure that the secondary should be 250mA, not 0.250mA
it uses 5670 triode and 6005 pentode tubes. so you were spot on :)

The kits re on the way, i'm sure the schematic is somewhere on the net, but it will arrive with the kits.


barackuda 12th April 2011 04:41 PM

What a stupid assumption from me in the previous post :D
read read read and then post reply :D :D :D

OK, so I wrote to Hammond with the specs I need,
They replied with this:

This amp is a single ended topology (one tube ) . ( I DON'T THINK SO when it says PUSH-PULL)
The recommended primary impedance is 5000 ohms. The suggested output transformer is:
1628SEA (please see the links below)
Hammond Mfg. - Universal - Single Ended - Tube Output Transformers - (125 Series)
Hammond Mfg. - "Classic" Single Ended Tube Output Transformers - (1627 - 1642 Series)

The power transformer is a difficult cross. Most of our product line uses full wave center tap, High voltage secondary's. This request is for a Full wave bridge.
Our closest match would be 363CX (using 1/2 of the secondary) at 250A .
The secondary transformer would be: (WHTA DO THEY MEAN BY "SECONDARY TRANS"?)
182L6 or
185D12 or
Hammond Mfg. - Toroid Power Transformer - (182 Series)
Hammond Mfg. - Power Transformers - Global Use - (185 Series)
Hammond Mfg. - Power Transformer - Dual Primary / Dual Secondary (266 Series)

So this is their reply.
Did anyone actually build the 8W Mono amps yet?
I had a good look on the picture on their page and when you look closely the power transformer for the K-16LS and the K-8LM have same stickers. Does this mean they are totally same?
If yes, could I use a power trans that somebody used in the 16W stereo kit?

Any help appreciated ( I can serve as a guiney (spell?) pig for these monoblocks :) for future builds.


mashaffer 12th April 2011 10:19 PM

For hammond it looks like 1609 or 1609A are the most appropriate for your OPTs although I would like to see more margin in the power handling but they should work fine.

Undoubtedly the kit needs 250mA rather than .250mA as you say.

For power his first suggestion seems to be the best that they can offer. Alternately you could use that PT and redesign your kit to use a full wave (two diode rather than the four diode bridge) and use the entire primary. Doing this would allow it to run quite cool.

Maybe there are some other transformer makers that you could look at. I would be surprised if a 200mA secondary were not enough for the B+ but a detailed look at your schematic would help.

barackuda 13th April 2011 06:39 AM

Thanks mashaffer,
still waiting for the kit to arrive, the schematic is inside, as soon as I will have it I will put up a picture.
I think it will be something like half of the K8-LS stereo which is somewhere here on the forum (I will find it, perhaps it helps).

rvrazvan 13th April 2011 09:05 AM

I bet you can find someone to wind you a transformer in your country for not alot of money. Poland is a great source for the output transformers and tubes. Also ukraine is a good source of russian tubes. they cost next to nothing.

.:: INDEL Sp. z o.o. ::.
they have output transformers and power transformers also. but first you need to wait for the kit so you'll know what you need.

barackuda 13th April 2011 09:14 AM

thanks for the suggestion, but I'm from Slovakia and I work in Netherlands, many days a week on business trips. I simply don't have the time to go and let some make me a trannie. I need ready made product :)))
But many thanks for suggestions.
I bet when I have the kit and will post the schematic it will be much clear...


barackuda 15th April 2011 09:35 PM

OK guys, here is the schematic....
I hope it can help the guru's over here to help me :)

Uploaded with

barackuda 18th April 2011 12:23 PM

Hello again
The kit arrived today (with 50 customs :( )
As I told before, I am not able to find appropriate transformer from Hammonds offering (due to lack of knowledge). Somehow I don't understand the specs provided by S5.
Can anyone help with this and my previous questions?
I will have a read thru the upgrade threads for the K-16LS and K-8LS and see what I can implement to mine.


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