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TL-404 hookup

151.197.207.8
Posted on August 31, 2009 at 09:18:19
mqracing
Manufacturer

Posts: 3314
Joined: June 29, 2000
Contributor
  Since: May 7, 2004
 for reference.


terminal #1 (black) is ground

terminal #3 (orange) is 4 ohms

terminal #4 (yellow) is 10 ohms

terminal #5 (white) is 50 ohms

terminal #6 (green) is 200 ohms

terminal #7 (red) is 500 ohms

terminal #8 (blue) 5000 ohms (goes to plate of tube)




parafeed only. Blocking cap must "in front of" terminal #8.



the nominal impedance ratios (with respect to the full winding) of the various taps are as follows;

terminal #3 is 1250:1

terminal #4 is 500:1

terminal #5 is 100:1

terminal #6 is 25:1

terminal #7 is 10:1



MSL






Builder of MagneQuest™ & Peerless™ transformers since 1989
RE: TL-404 suitability in Gordon's Bugle, posted on September 3, 2009 at 14:42:36
chrismercurio
Audiophile

Posts: 52
Joined: August 4, 2008
 Gordon, Mike, or anybody with an opinion,

On 11/19/04, Gordon Rankin said: (for parafeed Bugle conversion)
Putting a BCP 15 as the choke and the EXO45 as the output would be simple. The BCP 15 will drop about 25V which means the B+ needs to go up by that amount. Simply vary Cx till that happens. I would use like a 4-5uF/630V cap for the parallel feed cap. Also don't worry about the increased voltage on the input driver it should be fine.

Since the TL-404 is supposed to be good for ~2w, can it be used in a Bugle parafeed instead of the EXO-45?

I have one other question regarding making the Bugle an integrated. Can you put a 10k:10k transformer on the input followed by an attenuator? If this works I don't know if the series and parallel resistors at the input can be eliminated.

Thank you in advance for your help,

Chris

RE: TL-404 suitability in Gordon's Bugle, posted on September 4, 2009 at 01:21:40
mqracing
Manufacturer

Posts: 3314
Joined: June 29, 2000
Contributor
  Since: May 7, 2004
 Hi Chris:

I'd say yes to both. The TL-404 can handle 100vrms across it's primary...
it's nominal impedance will be determined by what load impedance (i.e., speaker load) you place on which tap. See the table in my post with the impedance ratios.

The advantage of the EXO-45 is that you can spec the core material and would have more choices. That and it has a direct 8 ohm secondary impedance which yields the nominal 5K primary impedance which is near book value for the std operating points for the 45 tube.

If you were able to swing to a plate choke with a bit more L than the BCP-15--- I think that would be a good move. Look at the Dowdy plate choke which is 40 mils at approx 125 henries. The Dowdy probably is not on our standard catalog listings but I do have some coil stock for these plate chokes.

The 10k:10K input trans with a 10K volume control across the secondary is a great way to make an "integrated" amp. You only need to double check and make sure that your source (for example cd player) has a low enough output impedance that the 10K is a suitably large input impedance.

There are several really great 10K volume controls out there to choose from. Check out the link I've put below... this looks sharp... by I have not seen it yet in person or listened to it...

I stock the Penny & Giles RF-15 volume control and have several other options availble including the Alps 10K pots.


have fun,

Mike








Builder of MagneQuest™ & Peerless™ transformers since 1989
RE: TL-404 suitability in Gordon's Bugle, posted on September 4, 2009 at 19:47:59
chrismercurio
Audiophile

Posts: 52
Joined: August 4, 2008
 Mike,

Thank you for answering my questions. I appreciate it.

Since the 404 is an autoformer I assumed that it was 5k for all taps. I would be using the 4 ohm tap for my GPA/ALTEC 604's which run between 5-7 ohms throughout their operating range with the impedance compensation network installed. I became interested in the 404 after hearing Doc's phenomenal headphone amp at a headphone gathering near me last month and thought it would be nice to have an output transformer that could drive a number of heaphones as well as my mains since I don't need a lot of power.

It still leaves the question about the series grid resistor of 1k at the input which I think needs to STAY, and the 100k resistor in parallel at the input which I think needs to go...but someone with an EE degree and more experience can offer a better opinion than I.

Thank you,

Chris

RE: TL-404 suitability in Gordon's Bugle, posted on September 8, 2009 at 00:09:32
Caucasian Blackplate
Industry Professional

Posts: 4445
Location: Seattke
Joined: June 18, 2004
 The 1k can stay, the 100k certainly goes.

In that schematic, there is another huge advantage to using something like the EXO-45 over the TL404. You can connect the primary of the parallel feed output transformer to a cap coming off the plate, then connect the bottom of the output transformer primary to the cathode, essentially minimizing the sonic impact of the cathode bypass cap.

A lot of effort was put into the big Bottlehead Studio headphone amp's power supply to allow this type of connection with an autoformer, and these efforts are not exactly convenient in a larger SET amp.

(Also, the TL404 is freaking huge and takes a reasonable bit of space to accommodate)

On the headphone front, you will want to look into DC heaters for both the driver and output tubes for headphone use. Remember, as you go up in taps on the TL-404, the noise floor will also come up. Hopefully I didn't scare you away from the project, but it's good to be clear on the requirements early on.

RE: TL-404 suitability in Gordon's Bugle, posted on September 8, 2009 at 15:47:57
braubeat
Audiophile

Posts: 56
Location: San Diego
Joined: May 20, 2005
 You can always ground the cathode of the 45 and supply a bias voltage to the grid. I bet this would sound awesome with the tl 404.
Michael

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